If people can take stuff out of delves, and affect other parts of the game, it’s not isolated.
If it were a collection of ever-increasing Torghast powers, and nothing can be taken out, then it is isolated.
If everyone does delves, I have to too, to keep up with the skill bracket. (And there was no content for the first 2 weeks, so people did delves.)
2-6 WAS the bracket for some people, just like how the deleted 0-10 key range was.
And arguably, more players are within the skill bracket of 2-6 (12-16) than 0-10.