Even tho I wasn't a big fan of Eureka when they first released it, I did enjoy it later on (after some nerfs tbf) in the expansion when there wasn't much else to do ingame. Dungeons are nice and neat and all, but they're not the type of thrilling/grinding/challenging content that keeps you playing over a period of months where there is nothing new added.

Ultimates were necessary imo, since they kept making EX-primals and savages easier to make it more accessible for the casual-ish crowd, which was an ok move for me personally. You might want to keep in mind that savage/ultimate releases, world races and streams in general are really good advertisement and probably get a good chunk of ppl interested and play the game.

So in the end idm getting less dungeons, but other types of content instead. Which is definetly not just Eureka/Citadel and Ultimates, but also Ishgard restoration, fishing boats, performance, advanced gpose and so on. All of this takes a lot of time and work and I would argue that ultimates take the least bc, well, most of the mechanics, boss-models and fights are already in the game and just need to be kinda re-worked.
Just because the new types of content aren't for one personally, doesn't make them magically unimportant in the greater scheme of the whole game.