I would suggest a rookie QB to groom, of which I think Darnold and Mayfield have those qualities - Mayfield has them in spades. Based on player interviews from his team and the Sr Bowl, Mayfield just has that magnetism about him that brings players confidence and you can see their level of play raised with that confidence. If he was 2 inches taller, he would be the runaway #1 pick with no one looking second-guessing it. But the perception of "height matters" with 6ft tall not being enough is a topic for another time.
Of FA, there really aren't any out there. We are speaking of bridge QBs only at this point. Even including a Cousins or a Smith, I see this FA crop as Game Managers. Bridgewater is the closest to maybe fitting into the mold of Mayfield/Darnold, but I'm really curious on how he recovers from injury. Is he the same guy we saw in college, or has he lost some confidence?
Of all QBs that I can think of, whether they'll ever be available, I submit these 10 QBs:
Current QBs: Brady, Rogers, Brees, Wilson, Palmer
Past QBs: Warner, Elway, Favre, Peyton, Otto Graham if you want to go back that far
My point is that there are leadership traits that a QB should bring to the table, particularly with this type of young team. Not all QBs have them, and that's fine. This CLE team desperately needs a QB that can not only manage the game, but ignite the team - someone who loves the game enough to study their opponents and are able to be the decision maker the team needs. That field general that the team will flock to, stand with, and fight for during the game.
I have never seen, or heard, this said about Cousins. JMHO, and I can be wrong. But I don't see it. He can manage the game, but I don't see him being that field general. He's not putting this team, or any team, on his shoulders to win a game.