IMO, I doubt that soft steel or overheating/annealing have anything at all to do with OSR.
If lack of barrel hardness is a contributor, degradation of the rifling inside the barrel would become apparent long before OSR. I would think that for OSR to occur, the lands would have to actually be harder than the rest of the barrel steel.
I will have to re-read this entire thread, but is it right that OSR is visable but not measurable?