Kenny will be the first to tell you that he lost muscle mass and strength. The 185 lbs Kenny may not have been able to move around as fast as the 145 lb Kenny however if the 185 lb Kenny caught the 145 lb Kenny and hit him, it would hurt a lot worse.
Joe Riggs did this as well. Joe Riggs fought at Heavy Weight, Light-Heavy Weight, Middle Weight and Welter Weight; just not all in the UFC.
If I fought at my weight now I would be a Heavy Weight. I could easily cut if not lose a little weight to put me in the Light-Heavy Weight. And I'm sure with proper cutting and training I could make Middle Weight. Welter Weight would be a hard go but on a 5'8" frame; not entirely impossible.
"IF I COME ... I'M BRINGING THE PAIN WITH ME"