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.