While likely correct in context, beware making such sweeping generalizations. It's a common conclusion to make - many people do - but it assumes that these competitors are racing to be racing, and not racing because they like to race their IT7s. In other words, you're assuming that if IT7 (or these others) were banned as a class that these competitors would "definitely" compete in ITA or at least another SCCA class, versus leaving racing entirely.
Likely, but not assured.
GA
Right, I'll go out a bit on a limb here and say that in the NE, where we resisted the IT7 pull for longer than we probably should have, it has resulted in more entries for the region.
I was one of the only guys duking it out in A. Then we did IT7. In spite of the economy etc, the number of RX-7s increased. More entries for the region, more fun for the racers. Sometimes the IT7 crowd (often) was larger than lots of other classes like ITC. 4 -5 cars was pretty 'normal'.
It's safe to say that if the cars had been left in A, MOST of the guys would simply not be racing. The cars are cheap, the racing is fun, and because they feel like they get a fair shake, they show up.
Now, you CAN say that they COULD be more competitive than they were in A, with better efforts, after all SOME IT7 guys were running near the front, and even grabbing a win when the rains were biblical. Some might suggest that they weren't 'true' competitors. (Thats a line in the sand that gets drawn to the level of convenience of whoever is drawing it!) On the other hand, running at that level required a pretty aggressive spending effort (I'd say ITA in the NE has some fast cars) and development effort, and I think that was beyond the scope of some of the guys. (most of the guys) And...at that level (the car I'm thinking of broke and set records across the NE at 9 different tracks)...a top RX-7 is STILL lucky to be gridded 4th in a 20 car ITA field.
It just aint competitive. The B move should have happened long ago, but even if it did happen the ITAC refuses to class the car at an appropriate weight... so whats the point of moving the car, changing wheels, just to be marginalized in another class? The classing powers that be failed this car.
So, the bottom line is that those classes exist to fill a need in the marketplace, and the net net is more money for the region and more guys racing...which, last I checked, was the point of the whole exercise.