Levis needs to sit and learn, but I don't think it works for the Vikings. Not with JJ needing to learn. I can't blame the Vikings at all for not signing Rodgers. But from what I can tell Tyler Huntley, Desmond Ridder, Teddy Bridgewater, Carson Wentz, and Easton Stick, are all free agents with no team. Considering the Vikings situation, I'd sign any of those guys before trading for Levis. And I don't think much of Wentz, and Stick has struggled as bad as Levis.
There's psychology here too. Picture this: We're 6 games into the season and the Vikings are 3-3, and JJ has looked good at times, and made rookie mistakes that cost them at least one game, maybe two. With Levis, there could be pressure wondering, "maybe young Will Levis is the guy? He has a bit more experience. Tennessee sucked, maybe it wasn't his fault? Put him in there and bench JJ!" That would be a total disaster IMO. So bad you don't want to even risk it, at all. But if the Vikings are in that same 3-3 situation with Huntley or Ridder on the bench, no one would be asking that. However, if JJ got hurt, the Vikings would at least have an experienced QB who has started before coming in to relieve him.
Then, around rounds 5+ they can draft a rookie who they can push to the practice squad/emergency QB. OR, another team will draft a QB, and cut someone they have on staff, and the Vikings can sign that person. All of these are likely better than signing Levis.
48 hours until the draft starts.