I think there is an argument to be made that he proved himself in the last 2 seasons and will succeed under other coaches. Same as it can be argued that his success was mostly tied to Harbaugh and that he will revert to his earlier form, therefore being still unproven.

ar·gu·a·ble (ärgy--bl) adj.: Open to argument

I could've said "arguably proven". Arguments can be made on both sides. I hope he succeeds, I like the guy. But I don't know for sure if he will.

Some people say that he wasn't successful before Harbaugh because he had to learn a different system every year. Does that mean he will struggle during his first year in KC learning Reid's system? If that's the case, will Andy Reid be patient enough to wait him out? He's been known to pull the plug on QBs relatively fast before.

Who knows?