The Saints are a fantastic example of taking this whole concept to a new level of absurdity. Why not pay your backup QB somewhere between 12 and 24 mil a year? After all he was almost good enough to compete with a couple of mediocre starters. That's what happens when you let your coach dictate personnel moves. You get the whole security blanket concept taken to another stratosphere.
I would argue that there is very little difference in where this Phins team would be with the league's best or worst backup QB. Perhaps they would have won a game and put themselves in a better position to make the playoffs. Does that really change the overall trajectory of this team this season? Except in some very rare cases, one which Dolphin fans are very familiar with, you aren't contending once your starter goes down. And if you need that backup to win games in the starter's absence you weren't contending in the first place.
The Pats were always lauded for their great development program, churning out all these starting caliber QBs as they learned behind Brady. And to their credit they do have a tremendous success rate and manage to find a competent starter about half the time. At the same time you have to ask what was the point of it all from the team's perspective? What did they gain from spending all this draft capital and investing all this time in these prospects?