Mewtwo's seemingly amazing grab might be the product of two things.
First, is that his roll canceled grab is very good, as first discovered by Abadango himself:
https://www.youtube.com/watch?v=rfdYyrBtf_0
Second, is that Mewtwo's improved run speed has made his grab much much better. If you watch the above video, or used Mewtwo before the speed buffs, there's a noticeable difference.
Mewtwo d-tilt is super good, but it loses to short hop aerials.
The missing piece of the puzzle in all of this is when Mewtwo is in disadvantage.
Mewtwo, when in neutral, and when on the offense, can feel absurdly powerful. When you're spacing the opponent out, and you're deflecting their projectiles, and you're getting d-tilt into fair juggles you're on top of the world.
But if the opponent is in your face, if you're getting juggled and they read your air dodge (having the fastest-recovering air dodge in the game comes with its own unique set of strengths and weaknesses), or if you just need to reset the situation it isn't so easy. If you watch Mewtwos play, they'll get these huge leads and then blow them instantly because Mewtwo got hit 4 times.
That's where the balance in Mewtwo lies.
Do I think M2 might be a bit too good? Kind of, yeah. I don't think that run speed buff was terribly necessary last patch, and it influences M2's matchups a lot more than one might think. However, Mewtwos aren't throwing around the term "glass cannon" just because it sounds cool, or like how Foxes in Melee use it because they get juggled by the other best characters in the game. There's a hard cap on how amazingly Mewtwo can defeat decision-making with sheer technical skill because, while its moves are amazing, they have very understandable weaknesses, and while Mewtwo overall is very good the character's drawbacks cannot be simply ignored by "playing well."