I won't swear, but posts like this make me to.. I can't go on top of the leaderboards? No, with stock RX8 i can't, which i thought it would be the case, but no, i have to 'tune' it (yea, we're all professional tuners now eh, just buy the most expensive option and you're a "tuner" maaan.. ), it is a joke, and just because this game is more serious then a NFS tittle, doesn't mean it met the standard of top sims, it can, but with opinions like yours it never will.
I seriously think you are just trying to find excuses for your poor driving performance.
IMHO the time trials are good as they are been setup right now. It is true that people will always find "the car" for the event and after that every body will start using it, however, upgrades that can be made for the cars is very limited.
There is practically no engine tuning possible for the RX-8, and in the KUSABI case you have to meticulously choose what parts to upgrade to have the best torque/horse-power output. This is a level of detail that just makes the game more challenging because you need to do your research, learning a few good stuff in the process.
"(yea, we're all professional tuners now eh, just buy the most expensive option and you're a "tuner" maaan.. )"
I think someone very mediocre minded will consider itself a GT tuner just buying parts, not that the default setup that comes with them will make your laps faster and put you a top of the leader board.
Analyzing the replays of the top guys with the data logger you can see that they are achieving some serious G-forces cornering and also optimal RPMs (They are good rev-matching BTW, not having a proper wheel with clutch is a huge disadvantage). That is only possible spending some time tuning your car.
A good driver is not just good at handling the car, he need to know how the car behaves and how to set it up to best suit every track/condition that he may encounter, even when pro-drivers don't do their setups them selves, the best of the best like the great Senna had a very close relationship with his engineers to have them setup their cars to their needs.
With that said, Gran Turismo, like any proper racing sim (iracing, rfactor, etc...) allow you to do tweaking of your cars. And to master the game, you have to be good at both, tweaking and driving, a top person on the leaderboar should have to be excellent at both.
... Time Trials are what kept me playing for over a year, while with GT5 I'm pretty much done the GT Life mode, and the game is losing appeal. We need Leaderboards for whatever car/track combo we choose. 
