That's not entirely correct; joker laps were originally introduced to reduce contact on track. The joker lap is less relevant on a wide circuit like Lydden, but on the tighter European tracks it provides a contact-free way of passing if you are stuck behind a slow car.
Fair point with regards to the cars though. I considered them "pure" in that there is still a lot of freedom in the builds (unlike a lot of Championships), but no doubt that they are modified to the point where they are far removed from the original car (which is a damn shame, as I'd love an AWD Fiesta!).