What were Denver's options?
Fangio has his job on the line. He needs to contend. Probably can fight for a playoff spot with a known quantity like Bridgewater. Does he have a chance to win a Superbowl--definitely not. But taking some unknown QB w potential is a very low Super Bowl chance as well.
Live to fight or find a better QB another day. Good Qbs are hard to find. How much of a value has Kirk Cousins been for the Vikings? I agree w your premise but think the realities of the NFL cause teams to find value in average but steady QBs.
The problem I have is teams that stay w Qbs too long. For example, Goff. I'm pretty certain everyone knows who he is as a player. He can't read defenses, can't go though progressions, and makes boneheaded mistakes. He's a career backup that has a chance to win a few games with great coaching and play calling. I'd much rather play a Davis Mills for half a season and see what he is than putting my success on Goff.