It is not pro/rel in the European sense but there is an element of pro/rel. An Americanized pro/rel. You can never have a traditional pro/rel in this country because the owners would never vote for it. But in my system, I think they'd be more open to it.
It's not pro/rel in any meaning of the term. Just because you call it that doesn't make it that.
UCF can call themselves the football national champions all they want, but no one really thinks that they are, and no matter how many times they say it it won't make it so. No matter how many times you call a system that allows a team that has been "relegated" to the fourth tier to still play teams in the top tier and still win the overall championship a pro/rel system it still won't be one.
You dont have to call it a pro/rel system if you don't want. As I said, it wouldn't be the same as in Europe. It would be an Americanized version which would allow for 40 teams/cities to be called "MLS," all with a theoretical chance to win the overall championship, but broken into a competitive tiers. MLS needs, for example, a city like Pittsburgh and the 2.5 million people that live within an hour or so to be interested in MLS. If the Riverhounds have a nice new stadium and are part of a world-class MLS with world megastars coming in a few times a year, that would create MLS fans here. MLS needs to involve as many cities as it can.