Pacing and simplicity is a big problem for people. Leveling through quests is terrible at both of them. Dungeons are fluid and fast (and potentially fun even). It’s far less demanding of a player to click LFD and click queue then it is to spam quests. It’s not about the speed of leveling, but about what it asks of the players efforts. It’s painful to do quests, however it’s simple and fun to do dungeon spam.
But yes, I agree. Everyone wants Blizzard to fix these problems, but the reality is they won’t so no one speaks of it, unfortunately. They instead speak of the problems directly at hand, i.e. LFD removal.