It's far more noticeable in Sports and I don't really want to talk much of Forza 7 as I'm waiting to play it more on the One X rather than on my One S, where I can really compare it far more fairly to Sports running on my Pro.
But I will say there is more use of 3D polygons for trackside details like tire walls in Forza, the cockpit in Forza is better animated too, nevermind the weather effects
In GT sports, drive up slowly to the marshals and see big jump in level of detail as you get close, it's like a throwback, to PS era
Car model and HDR wise I agree with you, it's ahead of anything else out there, but at big costs to the detail gfx used elsewhere in the game and features like dynamic weather.
PD used to be the best on the PS and PS2 (GT 3 is a showcase for the system and looked better than most 360 racers) , but they've lost that magic since the PS3 era and games like Project Cars 2 are pushing ahead with features like weather systems and patterns and AI (which is still poor in GT)