This is going to subjective, but he isn't a bad quarterback. He is a good quarterback. That's the problem though. He's a good quarterback, not a great one, and he's getting paid to be great. Plus, this is it with him. We are going into season 9 with him and we've seen his ceiling. It's a player that can win some games for you, no doubt, but when the going gets tough he crumbles.
Good defense rolls into town? He crumbles.
Big game? He crumbles.
Playoff game? He crumbles.
Just take this last playoff game against Green Bay as an example. Sure, the defense did him absolutely zero favors in that game, but he had his chances to drive his team down the field, and failed. Go back and watch it. Passes sailing all over. Passes low. Passes high. INTs. It wasn't good. When you're paid to be great, you need to be GREAT.
He'd be a perfect QB for a team that is trying to come up and win some games while building their roster. He is not a cornerstone franchise player.