I'll add my opinion FWIW.
Established starting QBs that are relatively unchallengeable for the position can cost upwards of 1/8th of a team's salary cap space. Elite QBs can burn up to 1/6th of that space. That's not on one position - that's on one player. To make the rest of the team competitive teams cannot afford to expend a whole lot more cap space on that single position. The days of Morrall backing up Unitas and then Griese, of Kubiak backing up Elway, etc are long gone.
The closest we've seen is Rodgers picked to back up Favre. Then we've seen NE picking guys like Mallet relatively early to back up Brady - but both those picks were made by far-sighted GMs who saw way too much value drop and refused to think conventionally. Even Rivers being picked in SD with Brees on the roster was due more to questions about Brees to become one of those unchallengeable guys.
So if a team has a QB that they consider unchallengeable - or relatively so - they are reluctant to burn a lot of cap, even at today's rookie cap limits on another QB. Plus it can create dissension if a QB controversy breaks out later.
One can make an argument that a higher draft pick can be trained into a marketable commodity later on, but then the team has to commit to training them and then being able to recover both the draft pick and the training time/cost on a more favorable draft pick. We've seen how difficult that is, though teams can do it at times.
But drafting a QB goes deeper than that. Teams rely on backup QBs to do more than hold a clipboard until an emergency comes up. They have to have credible arms/football intelligence/talent to assist in training other positions in OTAs, TC, and PS when they have to take a lot of reps, and during the season when prepping for next Sunday they may have to credibly run the scout team for the D. These guys are also sounding boards for the starters during practice and games, and do extensive film study looking for flaws in the other team's D. Hell, even holding for the K is an important task. Ask Tony Romo. Those are very important to critical tasks for the team.
So most times higher round picks on QBs indicate a team may be looking for their next starter - with the few notable exceptions, teams drafting QBs late are looking for a cheap but very important cog in the machine. I think some guys like writers don't understand how important the backup QB is to the team even if they don't take a single regular season game time snap. They aren't just the guy who has to step in because the starter got his bell rung - they do a whole lot more, and it is very valuable to the team.
It's critical to get the right guy for the job. Look at a guy like Sorgi who backed up Manning for years. Certainly not starter quality by any stretch, but very valuable to IND. Flynn has shown he struggles being THE guy, but adds great value to GB and can run the system very well in an emergency.
And every once in a great while - certainly the exception to the rule - those late guys can expand into starter/unchallengeable quality players. But that's icing on the cake, and almost certainly not why they were drafted initially.
So just because a team burns a late pick on a QB, it doesn't mean it is throwing that pick away. Only someone unfamiliar and uneducated with football would think that player doesn't add significant value - even if he doesn't play. Teams need the right guy in that role. So they use draft picks on them, even if the players may be more flawed. A guy in Emery's position ought to understand this if lunkheads like me can.
