Yes, I've noticed that too, though it isn't as simple as a slower car always levelling up faster, but a slower car can level up faster than a faster car. The game seems to compensate for the lower performance in a way that can over-compensate. In terms of levels per lap, a slower car might always level faster, the question is whether it's enough to level faster per minute, given the slower lap times. In my experience it can also take fewer minutes to get a slower car to level 50, whereas without whatever compensation happens, it should take longer as it's completing segments less frequently.
I did some multiplayer for the first time yesterday, just the first 3 qualifying races. At the end of that, it displayed some messages about the whole thing, and I noticed it said that it matches on skill rating first, then safety rating after that, which is the opposite way round to how Gran Turismo does it. My 3 races became progressively less like Wreckfest, but I think that was mainly due to qualifying better. The first race started early for some reason, so I hadn't got a qualifying lap in, and it took basically the entire race for things to settle down, as people ramming me kept me in the melee part of the field. 2nd race I instantly ran the qualifying laps in case it started early again, but ended up using mediums, so started lower down than I should have. 3rd race I at least did my instant qualifying laps on softs, so had my best grid position, but still lower than if I'd dared do some practice laps first. Neither of the 2nd and 3rd races started early like the 1st one did, so my haste in getting the qualifying laps in turned out to be unnecessary. I think I finished 5th, 4th, 2nd, getting S safety rating and 43xx skill rating.