MLS is trying to be profitable and watchable for every fan in North America, so it can't really have super teams dominate the field year in and out unlike Euro leagues. According to Wikipedia data they already command top 10 revenues by soccer leagues in the world, placing 7th (
List of professional sports leagues by revenue - Wikipedia).
According to
Football transfers, rumours, market values and news, they also have around the 10th highest market value in terms of player transfer value of leagues around the world, behind only 8 European leagues and the Brazilian Serie A.
Top vs Top team I think it ranks pretty low as most leagues will have their #1-2 giants, in an elimination style tournament with them they will always severely underperform. However league wide if they somehow merged with one of the bottom half of the top 10 Euro leagues their teams would probably fare fairly decently and not be total relegation fodder.
MLS gets wrecked in CCL mainly because they always play the top few Mexican giants - Monterrey, America, Tigres & Cruz Azul, all of whom would be relegation fodder in the EPL but would be fine mid table teams outside of the top 5 Euro leagues.
At its very best in the medium-far term, I think MLS could conceivably be among the low end of the top 5 Euro teams. But that is still far distance away from now and still plenty of work to do to get there.