It's the same with original cars, BMW M3 has all drivers named either "Mueller" or "Priaulx". Ferrari also has duplicates but less.
Well, anyway without mods using original GTR2 BMW M3, 12 lap race, x4 fuel usage and 19 cars i was following behind place 18th all the time, some of the cars pitted already at lap 3 (wtf?) and i went from 19th to 15th. Next couple of laps AI was pitting so i was 13th, 12th, 6th, 3rd (i didn't overtake a single car i was just driving slowly behind them) and when i was 3rd it was my time to pit, i didn't see the 2 cars in front until i enter the pit (1st and 2nd place were already there) so i added fuel til the end and i went from 3rd to 1st because they stayed in pit. That way i won the race with no single overtake from 19th to 1st with 20s gap. Idk what's the reason but pitstops in GTR2 are totally broken no matter what i try.