I think old GT and Horizon both scratch a very similar itch for a lot of people that GTS just doesn't. Something is bound to appear on the Sony platform to fill that hole. Some people just like cars, collecting, grinding upgrades, making liveries etc. Others just want to race/time trial. I don't think you can satisfy both particularly well in a single game. Horizon is good fun but as a racing game for the competitive player, it's pretty terrible.
I feel you are just dismissing what legacy fans wan't. Sure some wan't something like horizon and they are probably playing that. The rest want all the circuit racing of the old along with all the car crafting that went with it. No need to bump them off to the kids table. Or dismiss it as being any less competitive.
I'm just imagining a scaled down Japan with all sorts of mountain roads, metro areas, water, traffic, racing... I suppose it would take PD like 10 years to make something like that but it sounds glorious.
Sounds awful and not at all GT.