I'm seeing the same things:
Vet backup for several million vs. kid with the tools to step in and manage the game for minimum bucks, and with intriguing upside?
The same money that could be put toward a vet backup QB to ride the pine could pay a vet journeyman lineman who would see significant playing time. Cap vs. need considered, a wise choice.
As to the fourth round pick, poor expenditure of draft capital argument, and presuming he'd still be there a couple of rounds later, I disagree. He might have been taken at any point - we don't know. The other QB's on the board behind him - well, let's just say I'm not impressed beyond practice squad and camp arm potential.
Good pick. He can learn from Stafford, not only about football but how to manage life. Cooper Kupp can help there, too. This kid has some growing up to do and is among solid mentors.