I understand what you're saying... and while he may have been a bit blunt, he was right. You could change cars... or even switch to a MM car.. and you won't all-of-a-sudden find the plateau sitting in front of you disappear, and magically you start pealing seconds off your race time... it's certainly not the car.

If your car is driving how you like (i.e. doesn't oversteer, understeer, and you can push the car without it getting too upset), then it's time to start seriously watching the guys that are faster then you, and figure out where on the track are they pulling the trigger harder than you are, or where on the track they are keeping better corner speed than you... and work on those same skills.

There are many levels to this... and just because you have hit a plateau in your lap times, doesn't mean you are driving that car as fast as it can be driven.

How about posting a video of one of your races, and lets see with our eyes where we can spot some room for improvement.