I'm certain that is what he meant as well. Writing an action sequence in a script is pretty easy stuff. The writer determines the setting, those involved, how it may start, how it may end, and maybe throw in a few memorable actions, but they know going in that the actual choreography of what happens is in the director's hands, so they leave the fight scenes pretty skeletal. As for doubts concerning whether Cullen and Welker can still pass muster 20 years later, Cullen frequently does voice work for CN and he definitely sounds Prime. I can't speak for Welker, but it's voice acting, not lumberjacking. Unless he's sustained an injury or illness to his throat, I'm sure he can talk.