Fable was always on Xbox and PC, though. I don't see how having it stay there is evidence of some sort of RPG "explosion".I disagree, a few of these wouldn't have been made without Microsoft backing and funding. Avowed definitely and Fable of course.
And while Obsidian probably wouldn't have made Avowed without funding by Microsoft, they would have made some sort of RPG regardless, and it would have ended up on both Xbox and PC, so their contribution to the number of RPGs on those platforms would have been the same either way.
The purpose of these acquisitions wasn't to bring more RPGs to Xbox and PC, but to ensure that fewer RPGs release on Playstation.