I know some Broncos fans who are trying to spin this as being more about Siemian being unexpectedly good than Lynch being bad, but Siemian really isn't particularly good. If Lynch was even adequate, it would be his job, because Siemian isn't exactly putting up a huge roadblock at the position. He isn't one of the 25 best quarterbacks in the league.
Maybe someone else can correct me here, but wasn't Lynch always viewed as a multiple-year project? That was my understanding, and if so this really isn't on him; it would be on the Broncos for taking a multi-year project at QB as their first round pick. I'm skeptical of multi-year projects at QB in general, since I think if a guy is that far away you can't reasonably project pro success at all, but if you're going to do it at least do what the Pats did and use a later-round pick on a guy who's going to sit behind your starter for at least a couple years anyway.