Kit car?
You can field a car from already made pieces that make up a complete car, tools and pit setup.
You just have to follow the rules and your car will appear. Nothing is left out and there's nothing to figure out.
The winning teams and drivers are the best at the setup for the track, the weather and a bit of luck. Winning teams are the best at the details. You can't build something better because it's against the rules. It's exciting racing with lots of bumping and pushing but for me it does not draw my interest in the cars themselves.
This is a very different focus than building and fielding the best race car because you're better than the competition at engineering, design and then on to the setup and other details.
I would like to see a series where they have some safety rules, a minimum weight limit, a restricter plate for say 600 horse power and no other rules. Run any chassis, any engine, no electronic aids and track supplied pump gasoline. You'd see some real racing between cars of very different characteristics.