You mean differentiate on the driving skill and not who has the most cubic money?
Besides, it’s not the first race series to do that. Not much of an auto racing fan myself (MotoGP, please), but IROC comes to mind (Cameros for everyone!). Motorcycle Super Sport comes close, you can choose different manufacturers, but the bike has to be pretty close to stock. I’m sure bigger race fans can come up with other examples.
There's currently a big discussion about the future of LMP2 due to that sort of restrictive innovation, taking it closer to spec. Then there's the multitude of one-make series further down the ladder - certainly isn't a new phenomenon to have arbitrarily close cars from one or more manufacturers.
Besides, it’s not the first race series to do that. Not much of an auto racing fan myself (MotoGP, please), but IROC comes to mind (Cameros for everyone!). Motorcycle Super Sport comes close, you can choose different manufacturers, but the bike has to be pretty close to stock. I’m sure bigger race fans can come up with other examples.