I agree with the first half of your post, but I think you're placing too much stock in reaction speed. Good reaction speed is undoubtedly ideal for fighting games, but it's not what top players rely on to react to things. Top players can react super quick because they're anticipating an option.
M2K's reaction speed is far from elite but his he can dominate by reading their opponents and punishing accordingly.
And honestly, even above-average reaction speed (190ms) vs average (220ms) is imperceptible in most (if not all) cases. It's further complicated by the input buffer that
makes reacting to things outright impossible. If there is a meta shift, it'll be more on whether a character can deal with Joker's camping rather than gatekeeping any particular player's ability to compete based on their reaction speed.
I've seen many people undersell the value of reaction speed in these games, and I've heard the word anticipation before. But I think it's important to clarify that what you're reacting to in this game is not always the animation itself--actually
no one is able to consistently react to a frame 4 Snake f-tilt. What you're reacting to when you anticipate is the
setup for the animation; once you've played the game enough, you start to visualize hitboxes moving around and you have a good idea of what option your opponent wants to go for in a given situation, so you can just put yourself in position and then react to your opponent being in position. What you call "anticipation" is in fact game knowledge + reaction rather than pure "prediction." Reaction is a
big part of anticipation--at least 50% if not more.
Actually most of the reacting that happens in this game happens long before a hitbox pops out--top players are constantly spacing around each other by reacting to the other player's movement options and positioning.
Brawl and S4 were hallmark examples of reaction speed being absolutely king in all ways at a top level. ZeRo's ledgetrapping with Diddy that he was so famous for hinged almost entirely on his ability to snap-react to almost everything that you could do at ledge--you just can't get that kind of consistency on correctly guessing/reads. Tweek and ZeRo both played S4 in such a way that they could always react to 3/4 of the options that an opponent was likely to choose in a given situation. If they couldn't, they would back off, re-space, and try again. Their gameplans centered on finding such reactable situations in all game states.
Then we have Ultimate, where two things changed: 1) the increased input delay and lower overall lag (e.g., 3 frame jumpsquats) makes it much harder to react to raw animations, and 2) the neutral is based on dashing, and there are unreactable midrange dashing options. Do you remember MVD complaining that he didn't know what to do about Inkling neutral because dash attack was too fast to react to? Half of the time that Tweek complains about Ultimate, he's specifically complaining about how there are options that he can't react to; he calls Ultimate neutral full of "risky guesses," and that's why he says that he hates the game.
Don't get me wrong, reaction still matters a lot--Samsora's bait and punish style, ESAM and Light's aggression, etc., are all possible because of their extreme reaction times. Light has claimed before that he won't do anything if it isn't a reaction; ESAM similarly says that he bases most of his play on reactions and if he can't react (e.g., in an online setting), he can't consistently get the win.
When Nairo gets your ledge option 7 times in a row and ledgetraps you for 80%, do you think he's reading/predicting, or do you think he's putting himself in a position where he can punish 3/4 of your options and then reacting to the animation for which option you picked? It's the latter, hands down, and these top players will be the very first to tell you that.
m2k's reaction time is decidedly
not average; I don't know who spread that myth (probably m2k himself said something like that way back in the AIM days), but he has far above-average reaction time.
Having a super fast reaction time vs. having an average one feels like playing the game in slow motion. if you combine that natural physical strength with game knowledge, that's when you get a top player, and that's when you get the skill known commonly as anticipation. But! And this is important to say, I think that Ultimate is the best game in the series so far for limiting the power of reaction. This Tweek example is the one exception so far.
I think Leo's Joker will remain #1 for a while, if only because I have faith in aggressive Joker being strong (he has unreactable mixups in so many situations), but the more defensive Joker gets, the more I think Tweek's nautral reaction advantage will shine.
that high is a first-time thing (for me), but it's actually not too far off from his OrionStats ranking (#9, I believe?). I'm not sure if I can buy him being that high given that there hasn't been a single Mario that's been consistently phenomenal this season, but I don't think him being a top tier or even top 10 is outside the realm of reality if we're considering just how valuable his strengths are.
