TBH: I was a bit confused about this.
I missed the high day's of rF1. Got into simracing with rF2.
I've been a rF2 server admin and i've raced at other leagues. Never seen this... Never worked as it should. (i guess since rF1)
With rF2 it's not the way to do it.

Car class selection was always in the rfmod/Vmod. And since rF2 there are no rfm mismatches to worry about. Seems to be a problem in the rF1 day's.
What if a league want to mix EnduRacers P2 and Apex GT's or other combo's?
And it's not that user-friendly to get booted from the server.
I don't have time to race online that much anymore. So it's not a problem for me. For offline: the car classes are nicely done.
But if you want to avoid that your cars are going to be changed and repacked for league purposes. I would look at this for the future.