Peyton Manning says teams fail young QBs when forcing them to change coaches, systems

I can't agree with this. To simply put, I fully agree and understand with what Manning is saying. But at the sametime you have to have a level of competence in your coaches. You need coaches who are good enough to out coach opposition. To make gametime adjustments to expose weaknesses in opponents. Mismatches, covering your own weaknesses, etc.

We didn't see that with Rizzi anywhere on the field on either side of the ball. The defense started getting more pressures but the run defense didn't improve at any point hardly at all. Nothing worth noting anyways. The offense couldn't ever get in sync. We lacked discipline. A lot of it. Everywhere.

Depending on who the head coach is, retaining Kubiak would help to Mannings point, on the flip side of that we're opening the door that its possible that he was part of the problem, which I think is unlikely, but we can't rule it out.

I'd rather us just start fresh with a whole new coaching staff.
Yet, every QB that we all consider the "best" in terms of the position fall in line with what Manning is saying. I get what you are saying about what a coach does but this also ties into why QBs can't do the things that you describe. Mastery of the system allows you to be able, from the QB position, to diagnose so many different things that you are stating that coaches should be doing (which I do agree with). Like @Rouxble stated, Peyton Manning had the same OC his entire time in Indy because Tony Dungy was smart enough to know that the consistency in the system matters. He then brought that system to Denver. Drew Brees mastered the system that CSP put in for him. Tom Brady butted heads with Bruce Arians because he couldn't effectively run that system. What did he do? Brought in the New England system and the very next year, nothing about that offense said Bruce Arians. Probably why he stopped coaching..lol.

All of these systems aren't helpful to QBs but the thing is, these coaches think less about actual QB development because turnover at QB is just as bad as turnover at HC. QBs are no longer allowed to fail and succeed. We care more about instant success than development. That's why we are looking for "modern offenses" which actually caps what a QB does in the system, simplifies reads, and is more reliant on skill players (that's why we always talk about how 'elite" QBs needs weapons instead of making the talent around them better).

But even with all of this said, I get exactly what you are saying.