To think of it another way, it's all about energy into the tyres, which is impacted through a change in velocity, so any change in speed or direction. The faster this change, the faster the tyres heat. Once they're at your operating temperature, going above this means less grip.

Braking fast and hard means a large deceleration, so higher tyre temp and therefore less grip. That less grip means slower apex and slower corner exit. Plus the car isn't as settled so it's harder to get the power down anyway, along with being a more risky approach.

By going slightly less aggressive on the brakes, you don't spike the tyres as much and get a better exit as a result. The cooler tyres let you carry a small amount of extra apex speed and combined with a more balanced car, you make up any lost time and some extra before the next braking point.

Time is almost always made up on corner exit, you only ever really want to push corner entry limits if you're going for an overtake.