It's true, and it's why so many MMO's find themselves leaning into adding that grind to leveling, or a repetition in the end-game loop. The days of every developer taking a crack at creating a 'WOW killer' (and all of them failing) have thankfully past, I'm sure there are a bunch of traditional MMO's that are still trucking along nicely (Final Fantasy 15, Black Desert Online, the new Maple Story) but that sort of Quest Content driven game isn't so predominant nowadays (outside of nostalgia trips like WOW Classic and Runescape Classic). I can't say I miss them too much?