I think the NFL has flip-flopped. It used to be (in the mid 2000's) that you didn't want the big dumb QB. You wanted a smart guy who can run a west coast type offense and move the chains.
But in todays NFL we have changed - Now the smartest thing to do is to get the biggest, most athletic, hard working, strong-armed QB (even with all their issues) you can draft.
Then mold them into the player you want.
Because you can teach patience. You can teach how to read a defense. You can allow wisdom to come to them as they age.
But you can NOT teach arm strength. Or competitiveness. Or pocket awareness. Those things you either have, or you don't.
Personally, I thin Mac's #1 problem is arm strength. Maybe i'm wrong on that, but that's just my personal opinion from watching him play. And im NOT talking about deep balls. I see the lack of arm strength on intermediate throws. He thinks he can fit a ball into a tight window, but he can't. It's almost like he imitates what the strong arm QB's do but he doesnt realize he doesnt have that "oomph" to fit it in.
Take the INT in the pre-season for example. I know he didn't see the LB, but there are QB's with rocket arms that can laser this ball to the WR so fast that the LB isn't going to have a chance on it. Mac doesn't possess that rocket, so he needs to be a bit more careful in his throwing lanes.
This play (below) by Mahomes is similar.
Mahomes has to leave the pocket and throw on the run back toward the middle of the field.
But with his laser arm, he is able to fit the ball in to a very tight space with a receiver being draped by a CB.
Edit: Its the 2nd tweet video. Not the first.
All that to say, Mac can still be good. He just cant be mimicking big-armed QB's. He needs to be smart and methodical.
He needs to take the check downs when they're there, move the chains even with short throws, be crisp on his screen passes and slants, and let it rip when his guy has a step on the defender (at least a full step).
Same thing on this play (below). He tries to rifle it into the WR off his back foot. He just doesnt have the arm for that. He should have thrown it to his RB that was wide open in the flat and would have gotten at least 5 yards.