"But then he would still be as useless as he actually is, but I would have gone through a great deal of trouble making him."

Come on Toki. Rex, despite all evidence, doesn't think Toki is dumb. He just doesn't think things through all the way. It's Rex's duty to prod him in the right direction.

"If I were to make a mechanical beast I would make it vastly more impressive."

...Well, there's an idea...