Yeah, that's another thing about Mewtwo: his frame data is mediocre. His fastest ground move is his frame 6 jab which is pretty bad compared to all these other amazing frame 3 or less jabs the top tiers in this game have. His fastest aerial button comes out frame 6 which is ok, but when coupled with his 5 frame jumpsquat isn't that great. His range is even kind of overrated, too. Granted, dtilt and ftilt have nice ground zoning ability but he doesn't actually get much out of spacing them at the tip, besides stage positioning. Fair is decently disjointed but it's still smaller than most swordie aerials. Bair big but slow, and Nair is tiny.
So why is Mewtwo so good? My answer: his punish game. I think his punish game is the best in this entire cast. In a vacuum, the rewards he gets off of reads and punishes are probably not as good as Ryu (and possibly not better than ZSS either), but unlike those two, he actually has the ability to force approaches. That's a huge, essential part of his gameplan and imo is what overall makes his punish game better holistically than the two I mentioned. Ryu may kill you at 60, but a smart player can lame him out and in some matchups just refuse to play his game. This applies to ZSS to a lesser extent; her mobility helps her deal with projectiles and zoning better than Ryu, but her awkward neutral can still leave her susceptible. Mewtwo having a chargeable versatile projectile on top of one of the best reflectors in the game AND amazing mobility makes his crazy punishes (footstool disable shenanigans, fair near the ledge, surprise full shadow ball, upthrow/backthrow, any of his smash attacks) all the more deadly, because he has the best ability to actually consistently put his opponent in positions where he can land those punishes. Ryu and ZSS don't have that, not to the extent that Mewtwo does.
The price for all this bull****? Dying at 50 against rage. I think that's pretty fair.