Except, doing things like Lord of Vermillion or Eureka isn't doing "more than just what every other game does". It's executing on concepts that have likewise already been done in at least one other MMO, but with some design issues avoided and, often, even more issues newly added. They went to no effort to make any of their side-content particularly integral, to have it form cohesively from the surrounding game systems, or anything else. They went with an existing design staple (the level-cap hunting ground), sketched it out with their own paint, fleshed out some bits with franchise-traditional and genre-trope elements, and called it a day. Which is... exactly what any of those other MMOs you dismiss as uncreative do.
You'd be hard-pressed to make any particular content type unique to MMOs at this point except by making it uniquely well or uniquely poorly, so as long as the developers keep taking these things part by part and function by function, how about we start aiming for quality alongside that pretense to novelty?
Or at the very least if a content is really just to be treated as "tide-over", then let's not spend more resources on it than main content when far more efficient designs are available? If we're going to commit, commit fully (rather than leaving things like Diadem or Eureka grindy, haphazard, unpolished, and ultimately mere "side-content"), and if we're not, let's be efficient.
Then all the more reason to add longevity in the most efficient ways they can without resorting to joyless reward loops? Throwing in fatalistic defeatism does nothing to advance your argument here. Clearly, it is possible to a degree necessary to maintain profitability, and clearly any sub-based MMO's profitability has varied tremendously with their ability or inability to satisfy consumer appetites for content. The question is how best to do so, not whether it can be done to a reasonable degree.