What really bothers me is this isolated instance is the replacement of the relic grind, which was specifically designed to keep players going back to old content at a drawn out pace with a tangible reward. You could also only move forward on this grind. Even players unable to keep pace could reliably keep up a few steps behind as part of SE's catch-up patch designs. But it forced you to do multitudes of content across the game, keeping stuff active.
Eureka being an isolated zone for top tier gear verses being an alt route as we saw with say, PotD gear, means that many players will basically have to live in Eureka or never touch it at all to be in the higher ranked gear of the day. The alternative is Eureka being too easy, and everyone walks away over geared in a couple weeks, and the content dies across the board.
How many players do you think will get de-leveled once, proceed to rage at how unfair that is, and then never touch this place again?