Mythic + is only a problem because Blizzard wants Raids to be the most rewarding activity and the ultimate goal of every PVE player, but they need to get out of it, Mythic + is way more popular, and if raids can't keep players engaged then it's the raids that need to be changed/fixed.
If people don't wanna do raids, then the problem is the raid itself, not Mythic + or PVP. Blizzard devs should ask themselves: Why people don't wanna raid? Why do people think raids are not fun? Instead of... How can we make Mythic + less rewarding and enjoyable so people do raids?
We gotta adapt, the truth is that Mythic + is probably the activity that's keeping the most player subbed these days, without it, I'm sure the game would be in an even dire state. (Imagine if Pandaria or WOD had Mythic +)
Blizzard doesn't need to change something that's working (Mythic+ dungeons), they need to change what is not working (raids).