~87% of cars in GT7 can be acquired in ~1 hour of game time.
Oh, but I'm sick of the big three events. ~67% of cars can be acquired after one completion of the "embarrassing, slap in the face" Le Mans race which takes 40 minutes.
Oh, but I hate Le Mans. ~67% of cars can still be acquired after any 2 regular WTC 800 races with whatever Gr.3 car you want. And you have your choice of a dozen different tracks.
Oh, but I hate Gr.3 cars. Fine, you can get ~70% of cars after doing an hour or two of weekly challenges. Which may give out an even more expensive car you need, or you can flip and buy something else you want.
Gran Turismo always has been a sort of "RPG-style" racing game. A million ways to play it with a lot of content readily available, and some remaining content that takes a lot of effort to access.
You can play the game like Tommy_D mentioned, speeding through the main campaign and only doing the sort of minimum. You can play my "winding road" style which is a mix of racing, grinding, buying and tuning cars and engines, testing random cars, etc. You can try to collect every single car or recreate all kinds of fun historic racing grids. The catch is that you need to decide what you want to do with the game and frame everything you do around that. Do you want 20 copies of the Ferrari 250 GTO? Then you need to grind. Just like that "RPG" will take a ton of grinding to max out every character/critter/dragon/whatever.
I guess all the spineless members defending the poor game design may prefer that "RPG-style" over the Forza style of 600 cars readily available (remember too, the Forza games are guilty of the FOMO/time-locked content as well). There's nothing wrong with either approach, they're just different.