I get where you're coming from, but there are several things wrong with your argument.
For one, you're comparing a sim to two arcade games and a sim that hasn't even been brought out to retail. The sim you're comparing it to is basically the natural evolution of Need for Speed: Shit Shift, though I've heard it's starting to finally come along as a legitimate sim.
Secondly, saying that they should stop making GT because of long standing issues that don't even have to do with the number 1 aspect of sim racing. The driving. I agree that most of the engine sounds suck, the A.I. sucks (All sims have bad A.I. except for maybe the F1 series), the clutch is a joke, and the wheel support is mediocre. But the driving is top notch, the car selection (even with the Nissan clones) is second to none, and the real world tracks are as accurate as technologically possible.
It sounds like you just have Gran Turismo fatigue, because you seem to think that GT is so far behind other sim racers.
All sims have issues though:
Forza: Most real world tracks aren't that accurate compared to other sims that also use laser scanning. The engine sounds are exaggerated. Power slides are basically built into the physics to make things more dramatic for the player. Bad A.I. even with the Drivatars. A lot of the minute tweaking/tuning you can do is guesswork by Turn 10 because they can't isolate the data well enough yet.
iRacing: It's ugly. The subscription model is a ripoff. The car selection is terrible. The most recent tie model isn't on every car yet, and some cars handle like they're on ice for no reason. (You griped about PD having a small team, but iRacing's team is even smaller yet it's regarded as the best sim racer out)
Need for Speed: Shift: Fuck that series
Assetto Corsa: I'll reserve criticism since it's still in early access. (I really like it though)
I could point out all the great things each of the sims (including GT) I pointed out have, but that list would take me past my lunch hour. I'm sure you get the point though.