Steve Young (after Tampa Bay and the USFL) stumbled upon a nice situation, where he could backup Joe Montana, and learn how to be a pocket passer. In 1994, he finally became one.
It took a while, though, and for a moment, it looked like he would never break out of that "run first" mode, which pissed off Jerry Rice to no end. There were many times in 1991-1993 where Jerry Rice or John Taylor was about to break wide open in their routes, when Young would simply take off running. While some were happy with a 5 yard scramble, he missed many a 20+ yard passing opportunity, and that really showed its ugly face against the Cowboys in the playoffs.
After he got the crap beaten out of him against Philly in 1994 (big time ugly loss, and he was benched), that finally knocked some sense into him.
I pretty sure today's teams are going to be nearly that patient with run-first QB's. If anything, I'm surprised that Anthony Richardson is still even on the Colts' roster.