The whole "protect your investment" thing is usually a bunch of bullshit. If the QB is good, he's going to be fine whether you throw him in day 1 or wait 2-3 years. If he's not ready, then I question why you would spend a 1st round pick on somebody who is stuck on the bench when your team clearly can't afford that.

If the QB is Brock Osweiler, you can have him watch and learn from Peyton Manning for 3 seasons and he's still gonna be Brock Osweiler. Cases like Alex Smith, Aaron Rodgers, and Steve Young are rare and potentially misunderstood. Alex Smith had a shitty rookie year, but starting his second season he began his journey from slightly below league average to slightly above. Steve Young was on a dumpster fire team in Tampa Bay but immediately came in and was producing at a HOF level in relief for Joe Montana as early as his age 26 season (3rd year in the league - 10 TDs and 0 INTs in 3 starts). I don't think the fact that Alex Smith started day 1 changed the fact that he was always going to be a pretty mediocre QB, and I don't think the fact that Steve Young was riding the bench for several years helped him become a HOF QB.