Good to know I'm not the only person who noticed this. I'm far from a graphics' whore, but the car models in Forza Horizon -- an Xbox 360 title -- look just as good as the car models in PC3.
I have no desire to play a watered-down competitor to Forza, Forza Horizon and GRID. I already own and enjoy Forza 7 and Horizon 4, and GRID -- with XB1 controller settings I found on Reddit -- is the most enjoyable simcade racer I've played since Project Gotham Racing 2 for the original Xbox.