I think this has been far overcomplicated. Shouldn’t you almost always be on the limit of traction whether it’s braking or steering or acceleration? Using all available grip possible at each second? If you are, it’s physically impossible to go faster. There’s no additional grip available.
Brake hard and you are using as much traction as possible to slow the kart. As you transition to turn-in and apex, you’re coming off the brakes and applying throttle. The grip is always at it’s peak if you’re driving on the limit, you’re just distributing it to different applications through a corner.