"Slow in, fast out," is a useless phrase

I mean it. Because the line explains the wrong aspect. "First on the throttle gets the champaign," would be a better quippy quote that mentions what you're optimising for. Because that's just it. It doesn't matter how slow you're going in or how fast you're coming out of the turn, and it's a bad line because it opens with the most harmful part of driving quickly.

Generally these one line phrases are the kind of nonsense old farts can recite in an attempt to sound sage. It is good practise to optimise for corner exit, because generally cars accelerate far slower than they decelerate, but there's also so many examples of corners where the logic doesn't apply. Any high speed corner before a significant braking zone would be a good case study. By the time you've braked early to rotate the car for a full throttle sweep across the apex, the guy who's sent it in by coasting is already squared up for the braking zone following.