I think it breathed life into the game. With out it dungeons are pretty pointless. It offers more challenging content outside of raid.
I don’t think m+ has anything to do with killing wow. I feel the lack of fun casual stuff that has meaning is far more impactful. Also, they added all these grinds to an ageing player base that shockingly might not have time to do with their full time jobs and family.
I’ll just end this with this: account wide rep and progress to whatever dumb system they crap out again.