As someone who has played a couple dozen MMOs by this point, I can say that the issue facing FFXIV with stagnation in design is something all the MMOs that I've played (that stick around, anyway) have faced...
And it may be a fairly fatalistic view point, but I've yet to see an MMO really solve it.
People often cite WoW when talking innovation and such, but I've been playing that game off and on for over 12 years now...and you'd be surprised by how much of the "innovations" are just new coats of paint on the same old design.
Case in point - World Quests. Those are the daily quests the game has had since Burning Crusade (which launched in 2007), which are themselves a variation (once a day, higher individual payout per quest) on the repeatable quests that have been in the game since Vanilla. The big difference? They show up on the map and don't require that you talk to an NPC to begin and end it.
Gear drops from bosses drops went from RNG from the boss, to a mix of that and tokens, to a mix of that and gold, back to RNG from the boss (but you don't compete against others for it now, and there's additional RNG baked in...oh joy....). And now they're adding a token currency again. Round and round we go with the same old and a new coat of paint.
Artifacts are talents attached to a weapon, and now attached to one of three pieces of armor.
The point is, innovation rarely happens after the game has launched. It's not easy to do, and games that supposedly do it aren't doing it as much as people tend to think.
BUT...
New coats of shiny paint are fun (usually), so we tend to view additions of that kind in a favorable light and they seem like a bigger change than they actually are.
Once I started seeing these kinds of patterns, my expectations of dev teams shifted from wanting major innovation (which doesn't happen often and tends to fail in spectacular fashion as often as it succeeds, if not more frequently) to delivering consistency of a certain percentage of the things I already know I enjoy. I welcome innovation when it's good and adds to the game (rarely, if ever, if the "innovation" removes elements, as has been the case lately with WoW), but I've stopped expecting it from games that have already launched.