Pit doesn't have trouble killing.
He certainly isn't killing as fast as Mario here. Not unless the Mario is incapable of avoiding the Bair sweetspot. Even then, Fsmash kills about as early and is a freebie if we normal shield your Fsmash.
Arrows aren't used for follow ups. They are simply a way of forcing approaches and racking up damage while refreshing Pit's moveset. Fireballs are annoying but I wouldn't rate them over arrows in this matchup. Pit has a myriad of ways of dealing with Fireballs whether it's by reflecting them, using WoI to neutralize them or simply jabbing them. Also Pit does force Mario to approach, cape or no cape. Mario's fireballs and cape aren't enough to force an approach from Pit.
True, Mario does have to approach Pit due to the fact that he won't be caping EVERY arrow, but my point about Mario's fireballs was that we COULD use them as an approach method in this matchup despite your two reflectors. Arrows can be used for their normal purposes as well, but now you have to watch for the cape.
The purpose of fireballs in any matchup is to force a punishable action. Since we're chasing the fireball, you'll perform that punishable action to kill the fireball, and we follow-up with our punishment method. It could be jumping, shielding, spotdodging, or even getting hit. The one variable to this that Pit presents is wingdashing, but that's not that big of a deal either. If we throw a fireball and you Wingdash to cancel them out, the situation resets. Neither one of us takes damage. The only side-result is that we're probably a little closer to you. The other perfectly safe response is powershielding.
AR should not be used as a reflector, unless you're on the move or something. AR is primarily an attack and should be treated as such. If a Pit hits you or your shield with AR correctly there is no way Mario should be able to punish it, unless its like Up B OoS (I think that has invincibility frames or something), but even then that should only work if Pit messes up the spacing on AR. Also Mirror Shield doesn't have much ending lag. It has roughly the same amount as Mario's Cape unless you purposely leave it out longer, maybe less.
If Mario DIs out of AR if caught inside and immediately capes, IIRC it should reach Pit's outstretched arm and turn him around for punishment. That, and it has punishable ending lag.
And I was referring to Mirror Shield in the event that it reflects an object, or in this case a fireball. As far as I know, after reflecting, Mirror Shield suffers additional lag until the full reflecting animation is complete. Mario doesn't have this with cape.
AR outranges Cape. Also refer to my previous quoted answer as far as punishing AR goes. As for approaching with Fireballs, Pit can wingdash backwards, neutralize the fireball and possibly push back Mario thus resetting any possible advantage Mario could have gained from his approach. It's an ok approach but it's not really a big issue like you're making it seem.
It's not a gamebreaker, but in a matchup such as this, a reliable approach is key. Mario has one. Pit doesn't...not that I know of.
Mario does not seriously limit Pit's ability to camp. He does hinder it a bit because of Cape but to say he seriously limits it is a silly over exaggeration, especially given the amount of unpredictability and manuveurability Arrows actually have.
Explain. All I know is that he can hold them a bit longer to bait cape, turn around a few times to bring the same effect as DashDancing, or loop them. Other than that, they're pretty limited, especially since it can be caped on reaction in some situations. Others, simply shielded since we don't need to worry about you grabbing us afterward or anything.
Mario cannot gimp Pit unless the Pit player is ********. Mario has absolutely no answer to Pit's recovery if Pit chooses to recover really high similarly to Snake as he can use WoI far off stage with little to absolutely no risk of being gimped. Mario on the under hand has to worry about Bair offstage, WoP Fairs, FF Uairs, Mirror Shield and Arrows. Mario also doesn't have much options against a Pit that chooses to ledgecamp him aside from Fireballs so thats one more disadvantage to consider. Also, if you take stages into consideration Mario doesn't gain any advantage in counterpicks against Pit except on Yoshi's Island which should be a ban against most opponents anyway and against Mario it's not even that bad. Pit on the other hand has numerous stages where he can CP Mario.
That's true, Pit can recover as high as he wants, go under the stage, glide, and a few other things that would seemingly keep Mario from the gimp.
Unfortunately for you, Pit has to come back to the stage. Every character HAS to come back to the stage. It's not a matter of from what angle you come in or how high you do it; it's what weapons you have to defend yourself as you recover. Therein lies the problem with your Snake comparison. Snake has a ton of viable options after recovering high to protect himself from being instantly punished upon landing. Pit has AR and Dair, both are unsafe on Mario's shield. Going under the stage is great too as long as your opponent doesn't catch on quick enough...otherwise you're under the stage waiting for a stagespike when you re-surface. Your safest options appears to be glide, mainly because of the speed and maneuverability that it brings. Even then, Fludd, cape, fireballs, Usmash and aerials can all affect glide in some form or fashion and make Pit vulnerable to a gimp again, except now his arsenal is short a glide.
Against Pit's options, Mario has his cape for arrows though much less effective offstage, fireballs for if you try to come offstage to get us, cape for baiting that Mirror Shield once we're close to the stage, and our upB Stage-Spike. Also keep in mind that our Bair contests with the range of your aerials, and Mario CAN turn around offstage if the situation requires it. You have tools and we have tools. Writing off Mario's gimping ability is a pretty huge mistake, no matter how amazing your recovery is.
Imo Pit wins 60:40 on neutrals and probably better on any CP he chooses.
Despite my responses, I may now be leaning toward 55:45 Pit, to MAYBE 60:40, but pretty doubtful. What're Pit's CPs vs Mario? Ours is Yoshi's or probably a stage with a lower ceiling such as Halberd. Ban is probably Japes.
offstage all of pits aerials except for dair are useful, fair is a really good push to smack somebody against a stage or get them in a place where they cant recover, which would be especially useful against somebody like mario, who doesnt have a very high vertical recovery
It's rather fast though. Fast = harder to punish than slow like Pit's. I do see your point though.
i would expect at least one gimp against mario a game, while none from him, since the only real answer to our recovery for you gusy seems to be hitting us out of our WoI, which is pretty much the first thing every pit player learns to avoid
Not really. It's more about forcing that WoI, which is done with fireballs, Fludd, cape, and aerials. When I say cape, keep in mind that I mean capeglide -> aerial, cape for ledgestalling, caping arrows you may throw back at you, and of course caping you as you try to recover.
i think WoI ledgestalling would be extremely useful against your UpB as well
Probably. Cape can potentially throw off timing and upB can stage-spike in the event that your timing is off.
should never spam fireballs on 
