The minor character argument is dumb. Technically, all non F/D characters are sides. The only real exception is Rachel, as she is a key part of the story of D/F even if she has no actual scenes yet. Without her, a lot of the story wouldn't exist.
Jennifer has very few scenes. Elena has scenes, but aren't consistent. Cassandra is minor for sure. Georgina wasn't around for large parts of the game.
All the characters in the game, besides D/F, have vanished at one point or another. That alone tells me they're all minor/side characters. It'd be interesting if someone played through the game and counted scenes, not just sexual but when they were around MC/D.
Elena would be 1st, probably by a lot.
Georgina would probably be 2nd, again by a lot.
The rest? Probably relatively even. With the Martin scenes recently, he may actually be 3rd. Cassandra hasn't been around long enough, Jennifer is more or less Elena's fill-in. Olivia and Graham may be 4th. Margo and Ryan are last.
The others like the competition girls and Koko are very minor. I'd actually call them true minor characters and the rest side-characters.