Please no more Eureka!

[Reynhart]

If they truly wanted this to be only for a niche anyway, why take such a huge amount of time and who knows how much budget to create this?

Exactly, "no one knows how much budget", yet people claim that it's too much budget. As for the time, why should we care ? It didn't delay anything else, they took the time they wanted to make the content they seemed important to include in the game. They know that part of their playerbase wanted something different than the core formula, and they provided it. If you only care about "ressource efficiency", then we shouldn't have Savage, Ultimate or PvP, they could simply bring back more hard mode of existing dungeons, since they reuse a lot of existing assets.

Why put so much behind it including the relic without giving us another option to get it?

Why should another option be mandatory ? You don't have another option for PvP gear. You don't have another option for each primal weapon or mount, and you definitely don't have another option for Savage gear. What you don't want to do is Eureka being the only way to obtain a powerful weapon when you don't want to raid, and it's not. Tome gear provides every access you're in right to demand, that's all they're entitled to give you.

Why does that have hairstyles and emotes, while other niche content like the Ultimates have barely any rewards?

Because it's a big zone, and people should be rewarded for targeting the most NM available instead of always rotating the same ones.

Where is the content for the rest of the casual playerbase that makes up most of the games numbers? (And yes I mean complete new content, not the next ex primal)

Gold Saucer having new attractions is new contet, Secret Temple of Uznair is new content, Blue Mage is new content, unranked PvP is new content, all normal trials are new content.

Why would they create more and more niche content that costs much money and time when most of the playerbase wont play it?

They created two chains of contents for people willing to invest their skill, and one chain of content for people willing to invest their time. That's three content for the whole game, making it still largely a casual game.