I noticed. Numerical patterns are an OCD symptom of mine. A full round robin or two really does feel nice. And yes, watching me eat M&Ms or other small candies is either hilarious or cringe-inducing. But you're building a model that ignores the motives and contractual obligations of involved parties. The MLSPU has specific provisions about competitions and the games involved, and American MLS teams are obligated to participate in the USOC. When the league goes past 24, games will be cut against some teams in the other conference or series will be reduced to single games against certain conference opponents. I suspect and would prefer the latter, but the former is possible, too.
By that time maybe the obligation could no longer exist, specially if only MLS and USL are the only pro-leagues in USA, and the latter is mad of all MLS-owned/affiliated clubs.
In this case, "affiliate" is not a close relationship. It's much more similar to an independent club than to the MLS2 model. They generally have only a couple players with MLS contracts, and often none at all. MLS teams aren't required to send anyone, and affiliates aren't required to play who they get. In 2011, there were eleven USL and five NASL teams in the country, compared with sixteen MLS sides. As many MLS as the others combined. In 2016, there were fifteen USL teams that were not MLS B sides, and nine American NASL teams, with seventeen MLS clubs that participated in USOC; almost a 1:1.5 ratio. Those trends look quite good for minor league participation in USOC. Independent minor league soccer is healthier than ever.