True. Again, that's why the first Nogueira fight was so cool, because his striking was better than ever before and he even mixed in some kicks. But you're right, the fluidity of his movements, the speed and agility and flexibility, none of it was the same post-accident.
Especially in his early days, Mir was definitely one of the quicker HWs. I think that it was Rogan who said that Mir's uniqueness as a HW grappler was that he used "small man jiu-jitsu," i.e. focusing on technique and speed rather than position and power. And he was able to do that because he moved so well and was so quick despite being 6'3'' 240+.
When I was doing BJJ in high school, two of my friends were HUGE Mir fans. One of them started an account on here around the time of Mir's initial comeback when he was fat and fighting like shit, and he picked the name
mirsgut. The other friend put as his signature, "I jerk off to the thought of a 240lb Frank Mir." There was even a fun moment when I was rolling with one of them and I went for an omoplata, he was on his knees defending, and then I started reaching back for his foot and he immediately went, "You trying to Mir me?"
I had to admit that that's exactly what I was trying to do, and nowhere near as successfully