When Brawl started out, everyone went to whoever they felt was gonna be their favorite (or the best) character. While people kept playing, they started to lose to Snake so they used him to win tourneys since he was the best in the game back then. Once MK started beating Snake overall, some Snake mainers (and the people who wanted to main the best character) changed to MK and also started dominating heavily. Skills kept improving from there til this day, MK's still the best in the game, and people who lose vs MK no matter how much time and effort they put into that one single MU compared to every other MU in the game, changed their mains to MK because it was easier than Snake/Diddy/Wario whose MUs aren't as even as MK:MK (50:50).
The more tourneys happened back then, the more MK won, and the more people realized that MK was in a league of his own. Remember MK being in SS Tier due to tourney rep? That was the time people realized MK was way too good compared to all the other characters. As the best MKs lost to Snakes/Diddies/Warios/Falcos, as bored mains quit the game because it was the same old thing (MK beating them even if they put in all their effort), as frustrated mains stopped attending tourneys and as the MK hate grew and grew, some people stopped using MK and moved onto the characters who apparently had "even MUs" with him. Our current top-level-tourney winners in the metagame are a Snake main, a Diddy main, and an MK main. One level below is a noticeable amount of MK mains, with a couple of random joes here and there (Falco, Wario, Snake, Diddy, IC, Marth).
Think about this... A large amount of top-players are using MK. We can say that there's a saturation of MK mains... Why is MK the most saturated character, and why are the other characters not as dominant as MK? In MY opinion, it's because MK is a far larger "tourney-placing modifier" than the 2nd best character. People are calling these mainers "top-players" without keeping in mind that MK might be the reason they're doing so well (which should be obvious, he IS the best in the game)... What if their skills are lower than the other mainers who struggle to maintain their top-player status (should be obvious)? It would then mean that their tourney placings are what they are because of MK, which should be okay if MK had some sort of exploitable weakness that doesn't revolve around theoretical assumptions and can be exploited consistently during a match! Snake has cooldown on some moves and can be gimped, Diddy's bane is for someone who can use items better than him to come around and beat him in both item and non-item usage, Falco suffers from his fastfall and below-average recovery, and so on... If MK had an actually exploitable weakness, would these people actually do this good in tourneys and be considered "top-level players"?
To me, you need the data to build views and arguments. But sometimes the data might eman something, but our eyes might show us something different. Believe it or not, calculators give out faulty info when you try to punch in tougher equations at higher-leveled Math problems, but how can this be if calculators give out calculations and is all about data? Sometimes our own eyes can tell us something's wrong with the picture, even if everything else points to it being perfect.