No not plenty especially not in competitive play. Arceus with dark plate was supposed to be the guy but Mewtwo has not one but TWO mega forms one for dark types and defense allocated types (X) and one that's just overkill (Y). And with Mewtwo you never know which mega form or Z move you're going to get. To add on to that his speed is the highest in his tier only bested by Pheromosa who although has massive speed and attack stats has wet paper bag defense and can be OHKO by anything. Deoxys was the next best thing with its speed and attack versions but it has wet paper bag defense and Mewtwo Y or X can stop it let alone base form Mewtwo in 1v1. Same goes for Darkrai - Mewtwo X can kill Darkrai in one hit.
Mewtwo's typing and massive movepool also allows it to hit anything extremely hard for neutral damage (even if it doesn't hit super effectively). Mewtwo has not only the firepower to kill most things in 1 or 2 hits but also the bulk to take mad hits and keep moving.
8 generations later and they've yet to make a legendary Pokemon capable of shutting down Mewtwo. Mewtwo in competitive play either needs to be worn down by a STACKED team and/or the trainer has to be inexperienced. But if paired with a very consistent team, Mewtwo is even harder to stop. In the new generation Z moves make him even deadlier has he can now OHKO even the toughest counter.