I kind of doubt this. Polyphony is a notoriously slow developer, they took 6 years to make GT5 and it took them 4 years to make GT Sport, which had just 168 cars on release. I find it hard to believe they managed to make GT7 in 3 years while supporting GT Sport with quite a lot of DLC (the car count has doubled since release and the track count more than doubled). Only way I can see this being true is if GT7 is a cross gen game that builds on what is already in GT Sport, rather than a built from the ground up PS5 game.