I'm actually not against Formes when they're appropriate, even if its a 1st Gen Pokemon getting one. This has more to do with it not feeling right that Mewtwo, a manmade clone of Mew, can alter itself so drastically in the same way that more natural Pokemon like Rotom possessing machinery to change shape, Giratina changing it's body to adapt to different dimensions, or Castform altering itself to suit the weather- can.
It makes more sense that perhaps a new organization picked up Dr Fuji's work and out of pride attempted another Mew clone.
That said, either way, I don't get why Mewtwo's tail would change places to his head, or why an improved clone of Mew would have a tail on his head(no, it's not an elongated head, it's a tail).