Can't see how car count has anything to do with car detail. This is beyond any graphical discusion and more in line with money and staff count.
BTW, I think the graphical fidelity of Project CARS cars is unmatched. Not only the modelling is top of the line, the texture work, specially the interiors, is beyond competition. high AF and high AA help big time here.
Forza offers higher car detail AND higher car count than both DC/PC, while also being on a shorter dev cycle. T10/PG have released 4 full titles since Evo's last major project which is MS: Apocalypse.