This is a bad take. You've taken a specific situation and generalized it in an attempt to make bad reasoning, sound. Similarly, those that dismissed a young player with superior athletic ability based on conventional wisdom were wrong too.
Adama Traore had threat, massive threat that was always there. Only a fool could not see it. Sure, his end product was wonky (still not great but has improved) but he disrupted teams and had a certain set of skills that were unplayable, skills that were beyond that of other players in the league. The reason you wait on/nurture that type of situation is because if he does put it together then you've got something. This is not a situation where you wait out mistakes so the player is ultimately able to make the bench.
This is similar to early Walker and his brainfarts. You persist with that because the raw materials are such that when/if he becomes more consistent his ability will shut down your whole right flank. And if your manager cannot gameplan with 1 side of the field shutdown he is shit or you've got other problems.
Persisting with someone like KWP and hoping he puts it together gets you where? When/if he puts it together what do you have? When he hits top form what benefits does a team expect to derive?
I've only posed those last questions as a means of comparison and not given my opinion. Each can answer for themselves but I will say that at no point ever will KWP carry as much threat as Traore or be as defensively imposing as Walker and that just goes back to the raw materials.
So your initial point neglects to consider the upside and time relative to benefit of waiting on a young player and the opportunity cost therein.