I think this is correct. I've been to a few Oakland Roots matches and the support base is strong, the tickets cheap, shoehorned into a stadium not fit for purpose but no one cares -- it's a ton of fun -- probably no surprise given the abandonment of Oakland by the NFL (TWICE), the NHL, the NBA and, now it appears, MLB. You can't even get tickets to Sacramento Republic -- their fans are crazed. A lot of the joy of the lower leagues in the UK and I'd argue more based on the handful of League One matches I've been to which haven't been libraries but have been quieter by comparison.
I will say this -- Portland Timbers have a real support base as do Seattle Sounders. That's a real rivalry. The Atlanta side does too. And I'm sure others as well.
But for MLS generally -- my GOD -- the drums. The motherfucking, shit-ass drums. They never stop. They are close to worse than the vuvuzuealas or whatever those awful things were called. Where are the songs? Where is the banter? Why the fuck are there DRUMS? It's horrifying.