Nah, it's literally unfixable. They screwed up big time, and now it's too late to fix.

The only way they could fix it, is if they make the necessary changes to make parties of 8 viable. As of right now, they are not. Grinding monsters over and over again is NOT a viable way to level - it's just a waste of time. The only reason it's alright to do for the time being, is because of the train doing NM spawns. Once that goes away, and all you're left with is the grind, everyone under level 10 will be officially screwed.

Now as to why they won't do this - players who got to 20 will complain about how it's "unfair" that they had to go through the grind. They can't risk this backlash. They'd much rather deal with the players complaining about how Eureka now takes too long to do, and settle with it being another dead content in the game.