Their cars just all feel vaguely the same to me, and just not as good as the URD ones imo. This is most pronounced with the Porsche 992 I think, and seeing how notably the URD Porsche had Laurin Heinrich give feedback on the physics, I would assume that one is more "correct". Pretty sure I've said this before, but I don't think the RSS physics are bad or wrong, but the default setups seem very understeery and "safe" whereas VRC and URD cars are probably closer to race trim. I will say though, subjectively with the most recent physics update the 963 and M-Hybrid V8 feel much better, so if they've got an update like that in store for the GT3s then I could be convinced to switch to a full RSS GT3 lineup just so I don't have to BoP ****.
RSS also banned me from their discord even though I don't post there, which is super funny. They must have somebody lurking this thread and didn't like my posts