I'm not too into racing sim games but I did find project cars enjoyable so maybe that's a good sign that they did something right at least for me. These days I think many of the modern racing games can be considered sim games one way or another since they have all become so realistic.
While I agree that Project Cars does have an arcade element in it, I think it manages to balance that with the simulator aspect aswell. Wait and see what Gran Turismo 7 is like when that eventually gets unveiled, although that won't be till next year they're saying.