It really depends what the assist is and how the car is set up. TCS would often make the car slower around the entire track than not using it - but easier to control if you got into difficulties (but usually getting to that point means you've buggered a corner entry/exit anyhow). ABS was very car dependent (power/distribution/cooling wasn't uniform at all between cars and different upgrade levels) and it really depended on your driving style - you could control braking a lot better without it and more easily keep the brakes at their proper temp. ESP again, very car and car setup dependent.
The one assist that DID make you radically faster in Shift 1 (other than simply having more grip from running at 'normal' handling in order to use it) was the conventional "steering assist" which assisted by kicking in when the tyre was in a certain slip state (eg having the computer directly assess the state of the contact patch), rather than grip (simple wheelspin/speed difference) as with conventional TCS assist.
The one assist that DID make you radically faster in Shift 1 (other than simply having more grip from running at 'normal' handling in order to use it) was the conventional "steering assist" which assisted by kicking in when the tyre was in a certain slip state (eg having the computer directly assess the state of the contact patch), rather than grip (simple wheelspin/speed difference) as with conventional TCS assist.