not sure i agree.
with raiding, you only have 3 levels, and as we know LFR is pretty straightforward.
M+ gives you a system of progressive challenges. I happen to like it, in general.
Mythic difficulty really does start to ramp up in the low teens and kicks into a much higher gear, in my opinion 15/16+.
to get past that level, you need to play the game non-casually - fully optimized builds, all the consumes, optimized stats, ~bis gear, running all the weak auras, auto-marked mobs, most likely on comms.
the margin for error really shrinks at that point. it is beyond my willingness, patience, and (probably) ability to push much beyond 15/16.
while I am not interested in chasing FOTM, i think specs that the community think are b or c tier, i would likely avoid, just because I don’t run with my guild. we are very small and most of them aren’t that interested in M+ or they just don’t play enough to progress.
but again from a game design perspective, M+ is waaay better than the current state of pug BGs. i used to really enjoy BG heals. it is just a mess now.
so, M+ let’'s you hop on for an hour or two, run a few dungeons, get some gear and resources, and head on out.