Well all depends on what you're going for. It is the best psychic attacker, but Psychic is really only niche for Machamp solos or agaisnt Gengar raids if you have none with shadow ball, and doesnt have much use outside of those given Psychic's effectiveness profile. Ice beams got some use as the best ice attacker for now and theres a few defenders weak to it so it really comes down to do you have enough psychic types or ice types so this mewtwo can be used for the other
I'd recommend at least changing PC to Confusion, it has higher DPS than PC in all situations aside from when Psychic is resisted, and most pokemon you'd likely be using an Icebeam on against wont resist psychic.
