Easy to make claims but more and more of these guys are capable to step in and do good things these days. Only on CB do you still hear this idea that QBs need to wait their turn and preferably not start until their junior year or some crazy stuff like that.
And being 6'5 has nothing to do with mobility. There are plenty of bigger QBs who can get out and move. Maybe he's more of a pocket guy, but his lack of mobility isn't correlated to him being 6'5. That doesn't stop other guys.