Darnold doesn't yet know how to play QB in the NFL because he's been stuck on bad teams.
Put him on the Rams, given him a year under McVay and behind Stafford, and he'll become a much more competent NFL QB. He has the physical tools. The question that it always comes down to for young QBs is if they have the mental ability to rapidly read defenses, move the secondary with their eyes, stand in the pocket under the rush, throw to the right guy, adjust the O at the line, FEEL the rush, and understand that their job is to distribute the ball to the team's playmakers.... not to run with it unless you are a Lamar Jackson who is a great runner, but has no reasonable NFL game with out running the ball. Darnold isn't Jackson.