M+ is the most popular content per Blizzard’s own Poll. Mythic Raid, in just the last 2 weeks, has 472,220 logged parses per WCL with many estimates of active population at only around 2M, that’s a quarter of the playerbase.
Based on that, I’d say your assertion that the player base would be “better off without M+ and Mythic Raid” is dead wrong and while there might be a few that share that opinion, it’s a small minority that shouldn’t be catered to by the devs for “the health of the game.”