Along with other factors - intelligence ‘does’ help make a QB successful. If a guy is not smart enough to understand coverages and read defenses, he is going to be in trouble.
If a guy is too dumb to know when to not force a ball into double and triple coverage, or too dumb to tuck the ball away and scramble or get out of bounds, he is going to be in trouble.
Also, if a guy is too dumb to digest and completely understand the offense that coaches want to run, that hurts the football team. We saw that with Trubs where the offense had to be scaled back because he did not understand all of it.
Is intelligence a guarantee of success? No.
But I would damn sure rather have a QB with intelligence… than one without it.