As far as pure QB talent, my top 5 would be:
1. Joe Namath
2. Kenny Stabler
3. Richard Todd
4. AJ McCarron
5. Either Walter Lewis or Jeff Rutledge
JMHO.
Walter Lewis was a lot like Jalen IMO. Gifted runner, but the offense was very one dimensional when he was in the game.
He actually had a good first half of his last year passing, The accuracy started declining as the season went on, though. As an overall QB, I thought he was one of the better ones.