I mostly agree, and yes NHL is still niche in the US. But it's also more than
3x the revenue of MLS and did not have to convince US hockey fans to watch it instead of or addition to better hockey leagues worldwide when it grew to the size it is now. So I think MLS does need to adjust to grow in the US market.
BTW, I never before looked at the Wikipedia list linked above. It's kind of weird to think that the NHL is niche in the US but the fifth biggest league by revenue worldwide. I also was a bit taken aback to see MLS is placed as high as 10th on that list, but when I saw where it was placed among the competition it made sense.