Well written post, Bill. I concur with your assessment of what transpired but I too struggle with why it happened.
My take is that RJ just had the physical tools and coaching would not have changed what he was missing. This is contrary to what happened with JP and Trent. I think both suffered from having too many coaches, put into the fray well before they were ready and had a woeful OL. Without these factors to hinder them, I think either of them would have been adequate QBs for us and a good coach would have covered up their inadequacies (slow thinking for JP and gun-shy nature of Trent).
I suppose we should take this argument back to when Todd Collins was drafted. Perhaps we should have developed him better and we wouldn't have been in this absolute disaster of a QB situation since Kelly. I am in favor of drafting a QB high a few years before your franchise QB is spent. As an example, I would think both the Pats* and Colts ought to be thinking replacements in the next 2 drafts. Groom a new one for 2-3 years when Brady and Manning are close to retirement. Which is what we should have done 2-3 years before the end of Kelly's career