The issue is that Trey Lance is in Year 3 of arguably the most quarterback friendly offense in the NFL, and he still looked like an undrafted free agent out there. Going to a small school and getting injured doesn't explain that.
The 49ers even said publicly they were surprised Dallas (a.k.a., anyone) offered a 4th. A midround pick could have fetched OL or LB help to win now. Trading for a developmental 3rd string QB doesn't do that, and probably won't in the future. This isn't about risk/reward, it's about opportunity costs.
This might upset people, but this move shows that the Joneses are more focused on out-leveraging Dak's agent in contract negotiations at the moment than they are winning a Super Bowl.