Just like Vick and RGIII, if you keep them in the pocket and force them to beat you through the air, they all show that their passing is largely dependent on the threat of the run. That's why Mahomes is different. He can beat you running but he is a passer first. If you over play your pass defense, then he'll take off on you.

Jackson is probably the best throwing, running QB but he's still a running QB. If he ever gets injured, he'll be just like RGIII and struggle to make it at QB.