Are you basing your comparison on the Michigan (C8.R) and Darche (Porsche) from 2021? If so, then those are simply a different class of car; the physics for this tune are based (mostly) on the 2017 IMSA BoP specifications, which are significantly slower than the final year of GTLM competition and the current WEC GTE specifications. I would not
expect this car to perform at the level of those two URD mods.
By contrast, I've been practicing with this car against the 2014-2018 GTLM field (C7.R, 911 RSR 2018, Ford GT, BMW, Aston) and it stacks up pretty well. Indeed in the season which just wrapped up on SimRacingSystem the Ferrari needed a 5% restrictor vs the C7.R. I do have a separate 2021-spec 488 Evo GTE project in mind, but haven't really spent a lot of time on it; that would be the one that would be able to go head-to-head with the 2021 URD EGT cars.
I will not be using 3D models taken from other games, thanks.
Thanks for your comments, though; I'm always looking for ways to improve the tune (whether I ever get around to
doing the work or not...)