To be fair, end-game replayibility of WoD was non-existent. WoD had great leveling but very little after you reached max level. Legion had different order hall campaigns (despite overlaps) along with artifact quests which helped replaybility but at the same time Legion had horrible legion legendary acquisition until later Legion patches.
For folks that forgot, remember how it was actually easier to level a new X class from boost to max level (in Legion) to get a shot at the "right" legion legendary because bad luck protection wasn't a thing nor was there an actual Legion legendary vendor. Also the power gain from Legion Legendaries was fairly significant during Legion progression.
SL (so far) doesn't have as numerous campaigns compared to Legion (4 covenants instead of 12 order halls) but at least with legendaries it's more deterministic than the RNG fest we had initially with Legion. And at the very least, SL does have end-game content to do compared to WoD. Granted having end-game content versus wanting to engage in that end-game content is the current problem that SL has.