How does Ground SB vehicle selection work?

I was wondering because, to me, it seems that it goes by ranks, but there also seems to also be some sort of BR cap; how exactly does it work?

It seems a bit ridiculous that I get stuck in my 1935/38 vehicles, but certain other people get to pull in 1943 vehicles. So obviously, like most of the game, they’ve dropped any pretense to make these re-creation battles even though SIM is now the last place in the game where I can play Allied vehicles and only fight (but not really) Axis vehicles or Blue vs Red. I guess it would be fine if there was an event-type game mode that could take its place that was consistent.

I like Sim, it would be nice if some of its elements (like gunner sights) were incorporated into RB to make RB more of a hybrid between AB and SB (I’m sure some people will yell at me for having that opinion), but I don’t really care for some of the weird choices when it comes to the vehicles that fight each other because it doesn’t make sense to me. Someone, please explain.