Well, I flashed to the official 1.15 afterwards so that should be a moot point. Either way, the router was unusable in the post 1.20 firmware state and now works fine so take that for what you will.
I do appreciate the work you have done in here as I'm sure many others do, but the fact is that there are a lot of users out there for which the firmware "upgrade" did a lot of damage too...leaving them to live with the fact that they have to turn off functions, limit themselves to the 2.4 ghz band and simply disable stuff that they shouldn't have to in order to get a router to partially function and not with it's advertised functionality at that. If others choose not to use the flashback option, thats entirely up to them but this forum should be used to help others and if this fix works (which it does) then they should be given the option to do so if they choose.
My 2 cents....