That's a fine question, I reckon!
The hard-nosed rule is that TBO let the LRF through, and GT2 let the GTR through. Different classes, they're not competing. That said, though...
In Race 2, both the TBO and LRF are Silver-licenced, and while the LRF is *largely* able to pull away, I've seen a few times where there is little or nothing to separate them.
The LRF lines up on the front of the grid. If it's that much better, it should be able to pull away into the distance. If one or more of the LRF drivers can't put a gap between the TBO and themselves, then I'd consider them fair game to compete against. Seeing an FXO go against an FZ50 does definitely provide some entertainment. The FZ50 gets away on the straights, but it can be caught in the corners. It's a good battle, usually. I'm all for on-track battling, and if it's between two different classes, then so be it.. particularly in this circumstance.
Race 3 is a slightly different story. The GTRs really are significantly quicker in most places, except some of the SO City tracks. Even there, they're usually able to make quite a bit of a gap. Ultimately, the GTRs should be able to pull away into the sunset unhindered by the GT2s. I would treat a GTR as a blue flag, if it's coming up on you. You can generally tell the GTRs because they come from nowhere and park firmly on your bumper.