I haven't read the whole thread, but basically your proposed stat assumes that the pitcher is 100% responsible for every hit and earned run, and defense has no responsibility. That's just not true.
FIP and xFIP on the flip side take defense out of the equation entirely, which is also not 100% correct, but probably closer to it.
Dave Cameron on fangraphs said in a chat recently that maybe 30% RA9 and 70% FIP weighting is probably closer to accurate.