From a technological standpoint, his contribution is quite significant. Pixar. Advancements in visual and special effects. Digital editing. Digital photography (not the only one pushing it but he's the figurehead). the THX standard. Digital projection (again not the only one pushing it but the figurehead).
The guy has pushed the medium forward. I'm not saying we wouldn't have advanced in cinema and that he's the only one doing it.
I'm saying, without him, we might be a few years behind from where we are now...