Marth can't poke at fox without getting punished if you read him right and I seriously think you're underestimating fox's speed. And if Marth is in the air, good luck getting down without taking a lot of damage if the fox knows how to walk and read people right... on top that marth cannot follow up any attack that sends fox a little ways in the air because of fox's shine, his ff speed, his air dodge, and most importantly, his side b that you can cancel and make it impossible to punish. (I do think Marth v Fox is only 55-45 in fox's favor though)
If you READ him.
A fundamental fact of the game, if you're forced to read when somebody will attack in order to do anything, that's a situational disadvantage right there.
Why? Because that means you need to time it in order to be successful, and most of the time, the guy tossing out the poke is safe. Of course, this isn't always the case (for example, in some match-ups dtilt from Ganondorf is safe on block, but for a variety of reasons it almost never saves him, mostly because the margin of error for predicting him is too great in most match-ups).
Now let's look at Marth, he generally has 3 potential poking moves, dtilt, fair, and nair.
That automatically means something, if those moves have unique counters required, then the odds are against you predicting the right move automatically. If they've got different timings to be successful then it's the same factor, and what do you know, the answer is yes in both categories.
And then you gotta take this into account, Marth's aerial pokes can be used in multiple ways in terms of whether they're advanced then retreated, fast-falled, combo'd with something else (please note that in certain patterns, nair won't actually hit your shield, but it's still safe, and does zone, and you can fall into if you predict wrong, especially since it's got a second hitbox (third if you try to get behind), meaning you it can be used to react to what you do to a degree.
Then take into account the fact that marth can also vary these patterns further, by full-hopping (if not read, Marth can cover it) or using over b to stall for a bit. He also has the aerial mobility to make most of these options safe except on prediction.
And if you predict wrong? Marth's got a great punishing game, if you hit shield, dancing blade works very effectively, and at higher percents there's not a single move that you have which can't be dolphin slashed on shield (some on hit too), and it kills. Marth's also got a ton of other moves which will beat you out on reaction, retreating fair beats almost everything for example, uptilt also works for a lot of stuff, so does jab, so does dancing blade, retreating nair has it's uses.
Marth's pokes only leave him open when he's read, and you've gotta read him really well if the marth player is utilizing his options properly.
And after that, Marth's got a pretty good follow-up game, owing to tech-chasing (dancing blade) and the general properties of his moves being very safe, long ranged and very disjointed, allowing reading the opponent (in a far easier situation then above, and a far less vulnerable one) produce results. Juggle trapping against fox is fun btw (yes, Marth is vulnerable from below, but marth makes up for it in general by making everyone vulnerable to being below him). Shine stalling is beaten by proper timing (there are locations that you will get hit whether you shine stall or not), airdodging by timing and spacing (uair is a moving hitbox, it's more then possible to make sure the end hits, making it a guessing game which Marth has the advantage, and if you fall through him, he still has options), fastfalling is simply not enough, and side-b, are you sure it's not punishable, the hurtbox on that move is awefully far behind the hitbox, and properly spaced, certain options hit both (dancing blade can for example), not to mention that you've got plenty of warning.
Also, chaingrabs, especially buffed chaingrabs if he gets a grab in. They punish hard.
Off-stage, fox has major issues with recovery, and Marth edguards very well.
Sure, fox has his advantages, nice combos (oh, beware dolphin slash), hurts marth a lot from below, and marth is vulnerable to gimps.
However the overall problem is that Marth forces him to read him in order to actually approach (as in, make it so marth is in fox's safe melee zone, Marth has to move through fox's laser zone, but there is no true resistance there, just the probability of taking damage). Honestly, it's not even about speed, it's about ability to keep options open, and fox really doesn't have that. If he was fast enough that it was impossible to react to, that would be a different story, but he isn't.
And now for the part that brings this whole tangent back on topic and explains why this is important:
Ultimately, fox has the exact same issues against MK, he has to read MK to move so MK is in fox's melee safe zone, and MK punishes him for it, hard if he messes up. Sure, fox has tools, but he has to commit too much, and when that happens, MK ***** him.
Yes, if you read him like a book, you can win. And if my ganondorf reads your fox like a book, I can win too. Doesn't mean Ganondorf isn't bad at the match-up. The risk/reward factor is just too much against fox to consider him a counter or even a neutral against either, simply because he can hit hard, but the odds of him getting in at the top of the metagame are too low.
edit:
You aren't thinking very creatively and looking at what all the tools have to offer.
That's because the tools he has don't leave him with enough options open.
Not entirely. Sure some characters are like that, but many are not. Fox is not about pokes. He's about getting a single hit and then following that hit up over and over again.
Ummm... pew pew pew. That's fox's poke.
Projectiles and melee pokes are functionally similar in that they force people to approach. The problem with lasers here is Mk's/marth's safe melee zone begins before Fox's so he doesn't need to cover his approaches.
Pika's very similar as well so I'll talk about him here too... Fox has the explosive speed and quick punishing moves that Sonic doesn't have so he can quickly get in and his single dash dance is great. He also has a good walking speed that CF doesn't have. It let's him have much more control over his positioning than Sonic and CF do so he is actually able to follow up moves unlike them. He also can lead into his kill moves unlike Sonic, CF, and Pika. He also has very good aerial control, a great fall speed, and a crazy good side b that make it near impossible to follow up attacks or edge guard him. He's better than Pika in most ways except without the cg though he does combo very well at low percents... It just takes a level of reaction that not many people have.
Pikachu has methods of keeping his options open, QAC is probably one of the most important ones.
Look at CF in melee. He was low on the tier list for a long time until people realized how to play him.
Again, Captain Falcon has ways of keeping his options open while still being threatening, and then a very good follow-up game. Why do you think dash-dancing is so important in melee? It serves exactly this purpose, forcing people to commit then punishing the commitment. Sonic is much more like Melee Falcon then brawl fox.
SF is about pokes. This is not SF. This game used to be about pokes but that's the old metagame. Now it's about follow ups.
Pokes and follow-ups together both define the risk/reward system in smash. Follow-ups define what you get, pokes force the pace.
Not true, Fox can get inside of a whiffed or powershielded fair and dtilt with crazy timing. It's the same way MK can get into it. But Fox follows up moves on marth much better than near any other character.
With crazy time... aka READING, and there's a very small margin of error here.
By reading the opponent, I mean, reading his options. You put him into a position where he can do one of a couple things and then you can punish all of them after you see what they do. You can use that to get ratios.
Which fox is very bad at because he lacks pokes and zoning tools. Both MK and marth define the pacing of the match and they set the options available. Because he can't poke, and has to commit to everything, fox CAN'T do what you're suggesting in this match-up.
Fox is not lacking in move list and MK doesn't have a move list on another level. MK's fair and bair are eh. With buffered SDI they aren't great and he can't follow up those moves well period. MK's dair and uair however are fairly intense though they are not as great against fox as most characters. Fox relies on playing near your opponent, having them not know when you're going in, making them throw out a single move, and instant reacting to get inside that.
Except a smart opponent with these characters isn't gonna throw out an unsafe move unless the opponent is committed, so you gotta predict them. If you could maintain your options then it would be a different story but... dash-dancing in brawl sux.
If MK is in the air and whiffs a dair when fox is in a neutral enough position, he can jump up and hit him in the few frames of MK's lag. If you can force an airdodge because they think you're going at them, it's a free upsmash. And with mixing it up at a speed that is very hard to react to, you're going to catch them often doing nothing forcing them to want to throw more moves out creating holes to punish.
Fox can also count MK's jumps and if you know when they're going to land, you can run in, throw up a shield to powershield attacks and play your options from there.
MK on the other hand has a very hard time following up moves against fox, though he is the best at it. It becomes a chess game and IMO fox has the upper hand in it if you understand all the options. Fair also work wonders if you approach from the correct angle.
We get it, fox has options once inside, now get inside, please.
As for mk, he's fast too, and his options control a great deal more space and are often far more guaranteed anyway. In non-guarenteed situations, he can follow-up better because there are few safe options then against fox, it's a guessing game, but mk has the advantage in the guessing game.
1st that "random stuff" that MK can do will get punished every time because it's easy to see coming. If MK starts up a tornado, he should get upsmashed every single time because of fox's explosive speed. MK can't just force Fox to the edge. If he gets to close and does any move, he will get punished. And running away with fox is about the worst thing you can do. Granted if the MK is running away, the fox shouldn't chase but should shoot lasers to make the MK approach, but MK can't force fox against the edge of the stage.
What frame does tornado come out?
What frame do most of MK's moves come out?
I'm sorry but you don't understand the speed/punish style of play very well in this game and I don't think you understand the follow up game very well either if you think this game is about pokes. You don't understand what fox is capable of and you don't understand all the tools there are in this game.
So IMO 55-45 MK though there's potential for fox to move the matchup more in his favor.
So how exactly can fox threaten while maintaining his options, how can he force mk to do stuff so he can punish?