Well, take this into account:
None of the "aids" system in GT games - ABS, TCS, ASM - are "simulating" those very aids. They are simply assists for the driving model (suspension, tire slip, braking threshold…), not virtual representations of their real-life counterparts.
They are simply called like that because, well - comprehension, probably.
"TCS" is not simulating traction control. "ABS" is not simulating anti-brake lock systems. "ASM" is not simulating suspension roll assist. While "SRF" does not simulate anything, it is the One Assist To Rule Them All.
In my opinion, the cars in GT5/GT6 are have their real-life assists already "built-in". So, for example, there is vast difference when driving F430 on the Sport Hard tires with no assists and F40, simply because the F430 have both braking and traction assists of some kind already virtually simulated in their very model.
When you use driving assists in GT games, you are not "making" car more similar to its real-life counterpart (famous argument of "that car have ABS, so I am using ABS"), you are simply using a physical-engine driving assist which - I say it again - does not represent virtual simulation of such real-life assist, but it is simply a assists to the physics model.
Also, every single assist - TCS, ABS, ASM, SRF - influence all other assists as well, even if you have them disabled. For instance, having ABS at 1 will not only stop the tires from lockup, it will also improve traction (what TCS do) and suspension stability (what ASM do).
In my final opinion, the only proper setting for the traction control is zero (0), where you rely on the "built-in" suspension characteristics. Of course, you are more than free to use whatever suits you 👍