While still a fresh patch, I think that the movement and up air buffs for Mewtwo alone completely upgrade his game to a noticeable degree.
It used to be that Mewtwo had an above-average neutral. While lacking a quick jab, his decent ground movement combined with nice, long-raged pokes and counterpokes meant that he could go toe to toe with even effective neutral game characters like Ryu. His main weakness was rushdown, and the top tier could just simply overwhelm them.
Now, however, with Top 10 dash speed, he can actually outpace most rushdown characters, and the few he can't, he still has his long reach to rely on in combination. Sonic and Falcon might still be a ton of trouble, but Mewtwo runs almost as fast as Sheik now, and so attempts to just get in and wail at Mewtwo can be more comfortably spaced out. By just having a better dash, Mewtwo's entire neutral game (as well as advantage game) just grows in potential. Not to mention, having a better walk speed means being able to more effectively outspace and counter with well-timed smashes.
As for up air, one of Mewtwo's qualities as a character, for better or for worse, is that he's kind of a gambler. In order to get the maximum output, you have to take a few risks every so often, and before this meant the tables could be turned on Mewtwo due to one wrong move. However, with the new up air, Mewtwo has greater potential to reverse the momentum of a match back in his favor because it's just a very real threat. Imagine that you've knocked Mewtwo into the air, but you miss the follow-up. In the past, Mewtwo MIGHT be able to get some damage in, but his options were either very close range (fair, dair), or were mainly damage builders (old up air, nair). Now, if you happen to whiff your aerial assault and get caught above Mewtwo? That might just be the end of your stock right there. The gamble is more even now.