To be honest I think Wow can be easily compared for other reasons as well. I'm clearly a wow fan but it's because it does have some quality, even if it's "the worst mmorpg of all time". But that's beside the point.
Why is wow a worthy comparison beside both being p2p games? In WoW each expansion ACTUALLY did a lot of changes and not just minor tweaks or UI modifications: each class would get totally revamped skill sets, rotations, sometimes even new skill and lose older ones. As someone who played paladin since tbc, they changed so much in the years that they always feel like an entirely new class which isn't a bad thing (and literally the only reason why I bought Stormblood, but it wasn't enough)
But besides the class changes, new skills, new areas and other changes, think about what each expansion brought to us (some of the same features in one expansion also reappears in another, so I'll avoid naming it "twice")
TBC:
10-25 raids (down from 40)
Token system introduced
2 New races (Draenei and Blood elves)
Flying mounts
New Profession: Jewelcrafting.
With Jewelcrafting, armor slots for gems
Heroic Dungeons
WOTLK:
Introduction of Heroic Raids (with 10 man being normal and heroic being 25: it was changed later to have both 10 and 25 a normal and heroic version instead )
Massive PvP Region: Wintergrasp (with a raid boss inside for those who owned the area)
New class: Death Knight (with 3 specs, so it's technically 3 classes in one)
New Profession: Inscription
With Inscription, the introduction of Glyphs (aka, skill modifications
Barbershop
Phasing (I think at least it started here)
Cataclysm
Complete rework of the entire world (new quests, changed areas) and also being able to fly in Azeroth
2 New races (Goblin and Worgen)
New Class/Race Combo (human hunter, gnome priest, Troll Druid, Tauren Paladin, etc)
New Profession: Archaeology
Guild Levelling
Stats rework, with the introduction of the Mastery System (which is different for every spec)
Stat Reforging
MOP:
New Class (Monk, who can fulfill all 3 roles)
New Race (Pandaren)
Simplification of speccs (no more talent trees)
Introduction of Scenarios
Introduction of Challenge Mode (Aka Timed runs)
Pet Battle system (aka what LoV should've been!)
Cross realm areas
Black Market (aka RNG bidding)
Flex Raid (more to that in WoD)
WoD:
HD models for characters (A bit odd, but a nice thing)
Garrison System (It had potential on paper, it was just badly managed)
Cross-Realm Group Finder for all content
Introduction of Mythic Raiding and the changes to raid difficulties (TL;DR: Flex Raids are now easy mode, Heroic are Normal mode and Mythic is Heroic mode)
Proving Grounds for queue random heroics (not the best idea, but could've been expanded)
Legion
Artifact System (essentially relics, but better made and different for each specc. Oh and customizable too!)
New Class: Demon Hunter (with only 2 roles instead of 3)
Class Halls (mini garrisons, but not as intrusive)
Class Campaigns for each class
Wardrobe system (aka what FFXIV should strive for!)
Quests for each profession
Introduction of Mythic Dungeons with a scaling difficulty similar to Diablo 3 Great Rift system. It's challenge mode but with more loot.
Introduction of World Quests (essentially dailies, but they change every X hours and keep the world busy with different - and USEFUL - loot and AP)
As you can see, each Expansion at least tried to bring new stuff to the table and while a lot of the content was practically the same (new raids, new dungeons, new factions), they ALSO changed a lot of stuff and introduced new features to test them out. And I like these changes because even if I don't like them (and some I really didn't), I felt like I was playing an entirely new game! Just now I've replayed Frost Mage after a long pause since WOTLK and it plays NOTHING like before, same for druid or rogue (outlaw instead of combat) and many others.
In ffxiv, what really has changed? We NOW got those major job reworks we desperately needed - which is great, but did we really need to wait for an entire expansion for that? - but what else is different from ARR? Diadem? POTD? LoV?
SB promised to bring "new exciting content" at the cost of fewer dungeons, but so far all I'm seeing is the same old content with a new coat of paint: if they're going to do the same exact content patching like they did HW then I guess I'm drawing the line and move on.
If it was an f2p I could easily skip over this rambling, but I've played f2p with a tenth of the budget this game but with enough content to keep itself busy for enough time.
To sum my point: FFXIV barely seems to implement or change the game and instead brings more of the same. Meanwhile, other MMORPGs try to change and WoW is one big example of how each expansion, is quite literally an entirely new game.