More to the point of Fomula E, the degree of standardization is changing as the series progresses, with increasingly more aspects of the chassis and powertrain open to development.
Having a standard platform at the start made sense to minimize cost and bring in new competitors who don't want to spend the $200+ million a year like Formula 1 or WEC, where only 2 or 3 factory teams dominate and make for boring racing. Even a big company with a racing pedigree like Honda hasn't been able to field a competitive engine in F1.
As the formula matures they can start focusing on more areas of technical innovation.
> This regulation provided a level playing field in which driver skill and team effort should become the primary factor for success.
Compared with F1 now where some teams can (effectively) "pay to win".
.. and I say this as a McLaren fan (which, for those that don't follow F1, is a traditionally top F1 team that has had an absolutely woeful couple of years).
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.