M+ absolutely does bring a lot more to the table, but like I stated above, it also dampens raid progression. There's just not much incentive to go get AOTC other than an achievement/mount/title that a good amount of people pay for anyways.
There's got to be a way to synergize the two forms of endgame content. As of right now, raiding offers nothing in comparison. So instead of waiting once a week for a few months to progress through a raid, you're gonna come to a halt and ditch the moment you get your one or two BIS items.