GT4 was only one example. If you insist for other GTs, then for GT3, some of what mentioned above also applies there (forgot to mention that some of those below can apply to other GTs):
- Covering their incompetence of game design with rubberbanding in AI.
- Locking the players of the cars with not for sale cars, prize exclusive cars.
- Even if the events are many, those consist of repetitive events with only difference in cars and laps, or championship format/not.
- Terrible car sound.
And for GT3 alone the problems that should have been noted before:
- A step down in UX compared to previous games by removing menu and License shortcuts - something PD would pull much later consistently.
- The start of that horrible rally physics (not that GT2 was any better, but GT3 had different but what's carried until now), no excuses regardless of what era it was released.
- Frustrating event design like forcing you to race in Test Course in big number of laps several damn times.
- Track padding with Reverse being separated as "II".
- (iirc) Can't halt long-ass Championships.
- The pioneer of the gacha roulette system, at least in animation. Gotta repeat long-ass races to get the car you want with cars being locked there.
- etc.
GT was ahead because it was overrated. GT also had a bunch of things they were behind other than sounds, like customization (for color I mentioned above), damage, car interior, race grids being limited at 6, motorsport aspects such as teams, actual comprehensive tutorial compared to purely time trial Licenses, etc.
To justify any past GTs because of pretty short list of games that were anywhere near the franchise as an overall package was what feeds PD's delusions further and left those issues unnoticed.