And you'll note that leveling is considered a chore by many players, and if people can find a way to make it faster or cheese through it, they would. To the point the devs have given us story and level boosts. Now, they did make a point of asking you to at least look over the Unending Journey when you pop the story potion, because there's still a separation between the actual story that you get to see in the Unending Journey, and the billions of fetch quests we're supposed to drag ourselves though and that SE themselves said they'd look into weeding out in the future. So I can't even say that MSQ isn't content, just that it's badly designed and there's a lot of horrible fluff entangled with the actual content. That's why SE still asks you to look that over in the inn room. Leveling, though?
Leveling isn't content so much as it's a chore. AST, MCH and DRK all started at 30. RDM and SAM started at 50. I don't think we'll ever see any new proper jobs starting off at a lower level. And even BLU, not only can we have this exact same debate about it too, BLU itself isn't gated behind levels so much as enemy skills. So even BLU doesn't operate fully by this rule-set.
Those questions really aren't comparable though. They're on different scopes, even your own examples. But see the thing is, outside of Eureka, leveling actually does serve a point. Not even IC because RDM and SAM showed us that was rubbish as soon as you get your Soul Crystal, but OOC - you legitimately need to learn how to play your job, and we've seen some complaints about RDM and SAM starting as high as they did because it presented an overwhelming learning curve.to me, your question feels like its poking at the very fundamentals of this game's creation/existence. "why does FFxiv or Eureka exist?". to me that's the same as "why does Savage/Ultimate exist, or lalafells".
Leveling serves no such purpose in Eureka. It's points set in arbitrary times in your leveling process to gate story and aetheryte progress. Now, if they had actually tied the whole thing to your relic, with Krile saying something along the lines of "you need a stronger weapon to proceed because this place is unique, go talk to Gerolt", that would've been another story, and actually would've given the weapon meaning beyond a carrot to force people into Eureka for. They did it in PotD and HoH. But it doesn't work that way here. And with the challenge log giving as big a buff as it does, you can power through your leveling at a pretty impressive pace, making any justification leveling in that place had all the more hollow and false.
You need to grind the living daylight out of that place already. There's no good reason beyond artificial extension of the content's life to let you start that grind when you're about ready to leave the zone and proceed to the next one. Light grind in Pagos starts at 25 - you had probably seen several NMs and mutated enemies by then. You can only get Louhi's crystals from the NM fate starting at 34 - I have been to several Louhi NMs already and I have only hit 34 today. I have seen no crystals from it, obviously.
Leveling in Eureka is punishment. Nothing more.