All I can say is I do not have this problem. I just ran a race (single screen) with 10 of these cars at Zandvoort 2020 and the FPS never dropped below 100 and was smooth as silk. I have i7-10700K, RTX 2060 Super, 32G RAM, and most AC settings turned up. I saw someone was blaming the cars for being too high poly, but they have significantly less than the RSS 2021 Hybrid. By the way the braking of these cars is much improved by copying over the RSS brakes.ini settings.
However I believe you are not alone and that others have complained of similar problems. I'm just off to test a full grid.
EDIT: with a full grid, 90-100fps, very low CPU usage.