I'm not really sure what exact points are being argued in this TCS debate....but it sounds like a debate I've seen and been a part of before. So I'll give my two cents again:
Can you be fast with TCS on? Absolutely....I reached 65k DR using TCS2 back before I learned how to drive without it.
At that time, I was faster with TCS, but only because it prevented me from spinning, which would almost always happen in Gr.3 and even sometimes in Gr.4 cars.
Even if you are fast with TCS on, you are not going as fast as you possibly could with it off...assuming you've taken the time to learn to drive properly without it.
Some people who don't use TCS, probably should. What's better, spinning once in a race costing you 5-10 seconds, or using TCS and never spinning out? Or, even if you don't spin out, if you can't control the rear of the car when exiting tight corners, you're losing momentum and time, not to mention scorching your tires.
If you have some kind of weird opinion about TCS not being "real racing" or you just think you're too cool to use it even though you can't maintain lines through corners and exits....that's probably just your ego talking and you might be one of the people who should be using it.
So yes, you can be very quick using TCS, but there will always be potential to be quicker by turning it off. Even if you get your lines and steering perfect, TCS still engages during upshifts and loses you time for basically no reason. Even when you floor it in a straight line, TCS will kick in to prevent wheelspin, but with TCS off the car would have most likely still accelerated faster even taking the wheelspin into consideration. The problem is that TCS will kick in when wheelspin is detected even if you have partial traction there. When TCS kicks in, it's basically the same as lifting, so even though it's preventing wheelspin it's also reducing RPM's so the time you've saved by not spinning your wheels you're losing again by being further down the rev-bar, thus taking longer to reach the next gear and optimal speed before the next corner.
So in summary, TCS is slowing you down in small increments throughout the entire lap. If you can't control the throttle and the car well enough to avoid a spin or several near-spins, then TCS is the way to go and those small incremental losses aren't much compared to the time you'd lose by spinning. But if you can control the car well enough to not spin and maintain good lines while not letting the rear get away from you, then you're better off turning it off and gaining those several tenths per lap.
Also, TCS2 or nothing at all. No point in using anything higher than 2, and TCS1 doesn't prevent you from spinning so why have it on?
Thus concludes my novel on TCS