WoW was always designed so you could abandon quests if you weren't interested in them and move to a new zone, as long as you had the minimum level for it. That is not new; that is how WoW works. I was doing it all the way back in TBC. All that has changed is the pacing; in early WoW it would have been unheard of for a mid-level character to gain 5 levels in a day. Now it's quite easy to do it in either WoW or FF14 if you have a day off to play.
FF14 is just as irreverent toward its legacy content, unless you think for example that smashing through Labyrinth of the Ancients with a whole raid that's 70 item levels above the release sync is somehow respecting the fight design. It absolutely discourages you from legacy side content since there's no point taking up craftskills or (re)running optional dungeons to keep your armor updated when the combat is easy and the MSQ is going to give you free gear before you ever hit a serious pain point.
You are trying to compare dissimilar design philosophies to make points about pacing instead of simply looking at the pacing. I am a new player, I started in patch 5.3, and FF14 maintains the same rushed pacing, it's just obfuscated because it's running on the parallel track of being an MSQ-driven game instead of a story-optional quest-hub game.
Sure, if you drop quests in WoW as soon as you qualify for a new xpac, then it seems like you're speeding through the game. But the FF14 equivalent would be skipping cutscenes and mashing through dialogue, and that goes through the game just as fast. In both cases you're refusing to take an interest in the plotlines, exploration, worldbuilding, NPCs, etc. that the quests offer.
Both communities rush people to endgame, too, albeit for different reasons and by different ways. Do you really think the common mantra told to new players that they should "stick it out through the early game story because it's going to get really good in ShB" somehow isn't encouraging them to skip on experiencing legacy content?