I'm not 100% on 80s ATCC but I am pretty sure that teams at the top suffered in much the same way that they did in other countries with GrA rules. Once a manufacturer found the right combo of 4WD and turbo it was all over. First it was the Ford Sierra Cosworth, then the Nissan GT-R. Nobody else could compete and the usual happened when manufacturers stopped trying. DJR ran the Sierra for a number of years with great success until the Skyline GT-R came along.

One thing that fascinates me is how the various countries' touring car series evolved after the demise of GrA:

Australia went with it's beloved V8 RWD format and that evolved into Supercars, which still exists in a very similar form today.

Japan kept the Skylines and the multi-class structure, but banned the 4WD systems and allowed other manufacturers to build cars that could match the performance, eventually becoming much faster and more high tech. Super GT is probably one of the best examples of early BoP in GT racing.

Germany adopted DTM which was similarly more high tech. Ironically in the mid-2000s DTM needed a reset and based their new performance envelope on being competitive with V8 Supercars, but as they got faster and more expensive ended up unifying their rules with Super GT in Japan.

The UK held onto the 2.0 L touring cars and that became probably the most famous touring car series in the world. It was so popular that it was taken up as a second-tier series in many countries.

But as usual some series found trouble with spiralling costs and ended up dying off before being reborn yet again with tighter restrictions. Nowadays the BTCC is somewhat similar to TCR and GT3 is taking over a lot of series - DTM and GT300 have performance parity with GT3. About the only residual DNA from GrA that still remains is in Supercars, but those are being replaced next year with a new generation of cars, thankfully not GT3s though!