I think you're probably looking at Championship standard nowadays, in terms of quality but also competitiveness, I don't think it's the sort of League to enjoy semi-retirement any more. Maybe ten years ago but then I think they had to go down that route of getting big names in the early days to boost its legitimacy and get people interested in it and to be fair that model has worked.
Cosmos are in the NASL which is like the unofficial second tier over there but then cos there's no promotion from it or relegation from MLS, it doesn't really function as a second division as such. I think originally the idea was for that league to to be somewhere for teams not given a place in MLS to play and show they deserve a spot but now it seems to be trying to almost be a competitor in its own right, though I think established MLS folk would rather it gets turned it into a second division so they can get a pyramid system going instead.