Agree with HFS on it being a great, big Depends.
Balled up and wrapped, so you can't tell what's inside until you get your hands on it.
There are situations on track where you're glad for the assists. Heck, on a dry track, you always want ABS. (Whereas on a gravel track, you want it off)
But the effectiveness of TCS and ESC are dependent on many factors. You don't necessarily want TCS on cars with very little power or which suffer from bog on corner exits. And most everyday ESC systems are not very good. There are some cars we've tested that are faster with it off.
The 86/FRS is a special case. The grip limits of the car are so low compared to what the chassis can handle that keeping the ESC on keeps it happy. But it still slows you down in certain, tighter turns, where it should let you slide a little bit to get the car pointed where you want. We did slaloms wit the GT86 with ESC on and off. On, it was more steady, more stable and... slower. Off, the car was quicker, but it was very difficult to be consistent.
Over a dozen laps, or maybe a hundred, you will be more consistent with the ESC. And on the street, however fast or slow ESC makes you, it's better to lose a little speed in a turn here or there than to lose traction and enter terminal understeer or oversteer at the most inopportune times...