Technically it's true, but I can't agree with this argument. ADAC cars are the same as GTR3 ones, the only difference is class and liveries, and they can be used on ranked servers just like GTR3 cars. In terms of different cars, we only have three: 2012 model, 2015 model, and 2019 model. While there might be some confusion caused by the ADAC cars, I don't think that's a strong enough argument against adding an updated model.
Depends how the server is configured. I can´t use the ADAC20 Evos on servers or competitions restricted to Gt3 and I can´t use a different year ADAC car if the server doesn´t allow it meaning the need to buy multiple versions of the same car.