I think Ray has written one sentence that should be the control "let the drivers within a series decide if any car shouldn't be there".
As far as I can remember back, into the mid 60s every single time that the controlling body has taken a stand we have seen fewer cars and drivers.
As someone who will never take part at the level being talked about, but watch with interest, the F5000, and sorry Dale your group too, are so far away from "how they were" that I find them a disappointment, and I know from talking to owners and drivers, that the continuing development is hurting the fields. So as not to offend, what sort of HP did a 5000 back then, titanium components, a manufacturer advertising that they have supplied carbon wings and such, ever faster laptimes... These, the lap times don't come down by seconds a season from just being a better driver. Just ask Steve Ross, he has said he has spent too much, and now can't stay on the pace. A midfield 5000 at the McLaren Festival, would now be right at the back, and by some margin, still same (actually faster) laptimes, but the car is pure, just as it was "in the day". Probably won't come out again!