I agree. Rumble Falls is a HORRIBLE stage all-around. Even Temple is a more playable stage than that.
How can you say this when you were the same person who wanted us to take WarioWare seriously? I confess I haven't gotten a chance to play the friendlies there (though I haven't forgotten), but you were taken seriously. This claim suggests you have never played on Rumble Falls; good or bad it's obviously a lot better than Temple. On Temple, the winning strategy is dead obvious and totally degenerate. On Rumble Falls, there's real gameplay. How fair the stage is is somewhat non-obvious; I can't make a definitive claim, but what games I have managed to get people to play on this stage with me (it's hard) were non-broken.
I would point out that characters very good at jumping can avoid the main choke point by going around on the right off screen. Of course, they take "in the bubble" damage for that stunt, but it's a neat trick.
As per the whole idea of the choke point thing, it's not really as radical as it seems. Rainbow Cruise is an apt comparison actually. On Rainbow Cruise, you are pretty much forced to approach if you are counterclockwise relative to your enemy. On Rumble Falls, you are pretty much forced to approach if you are below the enemy. The main difference is the lack of a "boat" section on Rumble Falls and the fact that Rumble Falls is primarily vertical while Rainbow Cruise is mainly horizontal, but at least there's never a part as heavy with "jumping" as the middle part of Rainbow Cruise.
The spikes aren't really that deadly once you know the stage; the first one is pretty easy to tech, the second set just requires you to stay away while it's very high on the screen, and the third one is in a place where it basically does nothing.
There was one big candidate for abuse when this stage was discussed a while back. Notably, Kirby's and Meta Knight's up throws can be very powerful here. I did get in some testing back then, and it suggested that it was pretty reasonable to just be careful to avoid that. It's something to keep in mind, but I don't think it's a deal breaker.
The other hypothesis for "this stage is broken" was that Peach and Zelda fall too slowly to keep up during the "speed up" section of the course. I played around with them here a lot, and it's just not true. Peach's float kinda pushes her up during the "speed up" section (there's actually a weak force up in general it seems), and Zelda can just aim Farore's Wind low over platforms to not have problems. Actually, in general, aiming your jumps to end as low over platforms as possible kinda makes "speed up" really easy to handle in general. I also messed around with the great jumpers like Ganondorf and Bowser; they had a similarly easy time.
By the way, running forever here just plain doesn't work. You just go to the top of the screen as an approach. If they run, they have to run down, and then the stage forces them to approach into you. It's really not practical to run forever here, even if you are really fast against a really slow opponent. At least, that's what my experiences indicate.
Like I said earlier, it's pretty hard to get high quality opponents to play on Rumble Falls. It's very plausible that tactics develop here that end up being broken. I can only say what experience I have been able to develop suggests that the things that seem broken at a first glance really aren't. It's pretty unlikely this stage will ever get taken seriously and explored deeply, but it's not really so bad. I'm amazed people freak out over it while not freaking out nearly as much over Pirate Ship...
This, of course, is yet another example of taking someone posting a big list of stuff and then getting disagreed with on the thing people disagree with the most and feel most confident arguing against, instead of looking for common ground. Why, in response to that list, would we launch into a big discussion of Rumble Falls? I am not trying to claim the last word on it or anything, but it's probably for the good of all of us if we start to drift elsewhere.
I'm more curious what basis you conclude that those four stages have less of an "effect" on the match than the other candidate starter stages. Final Destination has a big "effect" when the Ice Climbers get their best stage in the first match. Basically, your list of four stages there (a common list) is a list of the four least interactive stages in the game. This seems "neutral", but it's really not. Certain characters (Ice Climbers, Snake, Olimar) benefit from non-interactive stages in general, and other characters (Mr. Game & Watch is the one I know well!) benefit from interactivity. I understand there tends to be a correlation between interactivity and total character bias, but it's not absolute. For maximum fairness, I strongly feel both philosophically and based on my own experiences that you need a seven stage starter list that includes states that interact a bit more. Adding Lylat Cruise, Pokemon Stadium 1, and Delfino Plaza or Halberd (pick one) really just makes the results all around better after stage striking, and I haven't seen even a single example of a matchup in which 5 stage striking produced better results. On that note, four stage starter lists are invalid by definition; it must be an odd number (for real fairness, you need an odd number other than three; I'll elaborate on this point if someone cares).
About mind focused on the stage, your mind should always be focused on the stage 100% of the time on every stage. It's present at every moment you are battling; seeing exactly what;s going on in the game is something you just do anyway. For my part, I just think of the fight as a coherent whole, and I am always looking for any element in the fight where I can get an advantage; I don't think of "this part is what the stage is doing" and "this part is what my opponent is doing". Also, given that every stage with one possible exception is insanely trivial to survive on completely undamaged for hours without an opponent present (the rain on WarioWare is the only tricky thing to avoid alone), I'm really not sure how the stages are threatening you. When you get hurt, it's all your opponent. Your opponent may do it by hitting you with a damaging move, or your opponent may have pressured or tricked you into a hazard. It's not really different; you get hurt when your opponent is succeeding. You don't just take damage out of nowhere or anything like that...