so why the devs never use 90% of the content for end game?

[Akibaws]

I would actually love hidden things to find after finishing MSQ. You could argue sightseeing logs are that, but if I could find like a rare glamour that would be cool.

[Raskbuck]

I'm personally tired of FATEs as a whole, because they basically consist of:
- Kill big enemy.
- Kill wave of small enemies.
- Collect items to turn in to NPC.

Sometimes they spruce things up, like making the FATE circle move while killing the wave of small enemies, but the core design has remained the same since ARR.

Bozja was just more FATEs, with the same design philosophy. Eureka was a decent attempt at making something different, before people found out killing NMs (aka, a Kill-big-enemy FATE) was more efficient to grind.

[Atelier-Bagur]

Eureka also introduced the follow the bunny for treasure kind of FATE. That was pretty cool imo