Gotta break the usual avoidance of rating race cars here to drop a SZ to the king.
The Porsche 962 is Group C. This car went almost a decade unchallenged and repeatedly beat down its competitors without any major updates or revisions. Jaguar went through XJRs like crazy, 5,7,9,11,12, same with Mazda and Mercedes. You know who was always there to challenge these new cars without fail until '94? The Porsche 962. Then afterwards they snuck it into the first year of GT1 and won again, then after that they cut it in half and made the 911 GT1, which dominated again. Not to speak of all the different 962 chassis which were converted into various WSC sports cars and the different uber-rare road versions. They may have struggled in the late 80s but they were still winning races up until the very end.
Across all the various series the 962 was entered in, it brought back 21 constructor's championships. You'd be hard pressed to find another car with that amount of silverware.
It's also my phone background at the moment.