Well, I played every GT title ever, since original title, with full completition, also.
I have a decent if not exactly state of the art setting (considering I completed GT original to GT6 on a controller, not sure is an important piece of the puzzle).
Still, can't win a handfull of races (still menu 47 to conclude because of the Fuji race and menu 49 because I don't really enjoy the Reb Bull thing)
Either way, the Fuji SF race is winnable and there are plenty of videos on youtube showing the way. Perhaps the same thing with the X2019 races, if I was interested.
Also, I struggle to get on the 5% delta to best times on the online Time Trials.
It's because the game is poorly designed? No, it's because there is much room to improvement on my skills, because I'm on a moment in my life I don't have the time or the energy I had 25 years younger, on PS1 times or simply on my 40s I can't keep up with people on their 20s.
That said, some races are harder today than 2 and a half years ago, specifically some of the "chili pepper" races, the ones using gr.3 machinery "Gr. 3 Cup", because only after update 1.40, about a year ago, the settings are restricted to BoP, before that the restrictions were based on PP limit, so you could set your car to match the PP instead of having almost every setting locked.
Notably, none of these races is needed to complete any of the menus, which woull get you pretty far above 11% completition.
In truth, I believe you only get a hard limit on PP value from menu 32 "Supras" (Race of Turbo Sports Cars) forward and real difficulties start effectivelly in menu 42.
Of course, it's your game and you progress the way you want, apart from the initial progressions, which is kind of enforced, but there are plenty of ways to progress over 11% without testing the waters on "chili pepper" events. It's like "Hey, there are about 200 events in the game, I'm 11% through it, I took a deep dive on the most difficult events in the game and struggle a lot!!! They should be easy for me because of my hability on previous titles with totally different physics and tire models!"