Damn, JinCa doing his best to try and downplay why Forza Horizon 5 looks better. He's gonna have to try harder though. It's weird that he would point out that "Project Cars had like 60k per car". Yet he didn't point out that DriveClub was 250k per car during gameplay. And that was 7 years ago. Project Cars =/= Forza Horizon 5 (or all other games).
Horizon Zero Dawn also lowers asset polygons during game play.
Racing games, during game play, won't have as many poly's per asset because the game is rendering more active assets at once. Forza Horizon 4 is an open world racer where 10's of thousands of assets are full destructible (and retained). They have 72 cars (plus drivatars). All the cars have cosmetic damage, which needs to be remembered and detailed for all 72 cars. Not only cosmetic damage, but functional (engine, suspension, tire, fuel) damage (more of a CPU hit).
There is also a GPU hit with custom liveries. FH4 allows you to add 4000 layers of liveries to EACH car on the tracks and in the open world. The game needs to display all of those for all people in the game as well as Drivatars.
With FH5 they have massive physics calculations going on as well. Something not found in HZD. Previous Forza games, the tire collision model had one area of contact with the track surface and refreshed at about 60 cycles per second. The new model that FH5 is using has eight points of contact with the track surface and runs at 360 cycles per second. That is a 48x jump in just the tire collision model itself, for every car.
FH5 has full animation IN GAME PLAY of suspension, damage, tire deformation, spoilers, dams, wings, wheels, character head, body and hands (including AI/drivatar cars), shifting, instrument panel. Crowds are also fully animated. Back when FM5 was released, the Vista cars were over a million polygons. Pretty sure they cut that in half when on the track.
And this is all before you add physics of weather, track heat, real time weather, suspension, engine, fuel, part wear.
And all of this and it's the most realistic and best looking game this gen so far.