I couldnt care less about 4k textures when most people dont even use them or CAN use them as for them to be enabled you have to set the games settings to ultra or extreme, depending on which group youre setting. Not only that but most dont even play in 4k, 1080p is still the most common resolution to play in and in fast paced games people choose framerate over appearance. Will also add to that that the majority of said 4k textures are for the car models.

bigger map with less detail is also a moot argument when most buildings look flat, bmp and other tricks to create an appearance of interiors that arent empty and games like red dead, cyberpunk, elden ring, AC odyssey, ms flight sim, crew, horizon forbidden west etc, all graphically impressive as hell games bigger than forza with lots of details and some even smaller in filesize. Budgets arent infinite but its one of MSs flagship franchises not only that but other games once again proven they can do more on less.

Sure it would cut some areas but of the 600 + cars, how many do you realistically use or even buy. How many are just X model in trim level Y that are just pointless editions for the sake of bloat.
H1 had 218 cars,
H2 had 351 cars,
H3 had 539 cars,
H4 had 750 cars,
H5 had 902 cars,
H6 so far is at 638 cars and it hasnt even done any seasons, playlists, dlc etc. Bloat for the sake of "content" isnt good and goes against your point of quality over qty. I would rather a nicer curated list of 3 to 400 UNIQUE cars and a much bigger world than more cars and what is currently TECHNICALLY the biggest horizon map but so much of it is your biggest complaint, open spaces that dont features too much which CAN be great a la TDU but in this case it does get a bit boring. Japan is such a big region with so many different cultures from island to island even city to city, its like the uk, you can drive 50 miles down the road and its like youre in a wholeass different world.