I'd say the opposite is true in regards to the exodus, at least from people I know. The grass isn't always greener, as the saying goes. XIV has a great story but many systems in the end game are quite shallow beyond an initial set of rewards (and if you don't want to do excessive grinding of every relic or getting achievements that require 1000s of collectibles turned in, for example). GW2 and other MMOs, while they've survived, have their own content cycles and ultimately their own quirks.
It's easy to pick on FFXIV and the community for selling the game as the best thing since sliced bread... but when you actually get past that initial learning curve and new player experience/feeling, you soon seen the flaws and areas of contention between developer and player. Class reworks are a strong area in which SE make changes that seemingly piss everyone off. Housing systems and various issues around it are a well beaten horse at this stage. Even the underlying server infrastructure and limitations placed on the game due to it are tired discussions at this stage. Any Viera or Hrothgar hat enjoyers in chat? The only advantage XIV has is age in that it's not yet reached the stage in which players just get aggressive towards the developers for repeat failing which is pretty much identical to WoW when it was at the same stage in it's lifecycle. If I had to make a prediction, long standing issues are only going to drive more toxicity between the developers and players of this game in the future.
There's also a few new MMOs on the horizon as well that'll throw themselves into the mix. Blue Protocol is due next year which is a Bandai Namco game being published alongside Amazon. There's the Riot Games MMO which is mostly a mystery but if they nail it like they nailed LoL and Valorant, it's going to be huge. Sony are producing "live service" titles under PlayStation with the fast being The Last of Us. They might not be MMOs in the traditional sense but they still tick a lot of the boxes even if they're closer to being like Destiny 2 or GTA Online than a traditional subscription based title.