I think overall MLS is really remarkable for what they have achieved.
I think they have done a good job, for the most part, up to now. But I think they are at an important inflection point WRT how they grow. More to the point, they cannot continue to rely on expansion fees as a major source of revenue. They're at 28 right now, with St Louis and (maybe) Sacramento on the way next year. How many more viable markets are there before expansion becomes little more than a Ponzi scheme?
The most obvious area for growth is in TV viewership, and as I discussed earlier in this thread they really need players/teams that will draw viewership on a national level. That's one area where AppleTV+ could help...anyone in the US should be able to watch any game they want, if they are willing to pay for it. But since this deal is locked in for the next decade, their revenues are likely baked in for that long (unless there's some sort of revenue-sharing arrangement with Apple that hasn't been reported). If they can still cut a deal with ESPN/FOX, and for a shorter period like 5 years instead of 10, that could give them a needed opportunity to go back to bidding at least part of their TV rights sooner, which could be great.....IF they can get the growth in viewership they need. But like you said, that will come down to them being able to have more marketable names/stars, which they don't seem to embrace at this point.