[eftychis]

I am not sure what you mean by "never used as is."

The Kelly criterion is an optimization of capital growth (its logarithm) method/guide. Not using it doesn't change its correctness.

But yes you need to know the advantage/the edge you have. Like with pricing methods eg for European options for Black Scholes you need to know the volatility and there is no way to know it, you estimate. This is where all the adjusting for bias and ML comes in.

[wenc]

But do you calibrate p (say through estimation) and then apply the Kelly criterion in your portfolio?

I don’t think it is used in this way. It swings too much with a given p.

[uoaei]

You calibrate for a reasonable distribution of p and use that to estimate (Monte Carlo, etc.) expected gain, optimizing your investment based on that. With this technique your estimate will probably end up somewhere around the common heuristics.