How about instead of increasing or completely removing the limitation adding
"legendary booster cards" they are golden shiny?
What it does? (only for LV 299)
It boost's up your car entirely from 16 to 17 but it gives you a permanent boost to come close to a 300+.
How long they would be installed in a car?
It can be limited for few races or limited for 7 days.
(Or permanent instead so each car gets unique at tuning?)
How do I get these cards?
Simply from the tuning shop but they are rare to get.
Also you can get these cards everytime but only one legendary set can be activated for each car
What about the effects?
They are doubled and also gives your car a set bonus, of course not to much to outperform everything.
So the limitation would be still there as they wanted but bringing a legendary card set into the game would be great LV 299 cars gain a boost up to match those cars.
A system like this not exactly, could solve the problem I guess.