Yeah there is something wrong with it. It doesn't really feel like a prototype at all, but rather a fast GT car. When you compare it to the 963 it doesn't even feel like they are part of the same class really, although the lap times aren't wildly different.
Its default setup is kinda weird, particularly the toe values that are wild. I haven't exactly figured out how to "fix" it completely, but made it a lot better by basically setting it up like a FWD car in FM7. Max front aero, minimum rear aero, swaybars at 1 front and 40 rear, 80+/0 in the diff, and then I cranked some anti-squat into it. Do that stuff to any other modern prototype and it will be undriveable, but the Cadillac will still understeer... just not nearly as bad.
I don't totally hate it really though, kinda. Like yeah it isn't as "sharp" as a prototype should be, but it also means it isn't as edgy feeling and it's incredibly stable. That means, depending on the circuit a bit, it can be a little less... stressful or tiring to drive or something, when compared to the other modern LMP1/DPi etc... But then at other circuits it's just frustrating to drive because you are fighting the lack of rotation the whole time.
The Caddy DPi is a much more "normal" prototype experience.