Agreed, all PCs will have competence roughly equal with their [power] level.
Agreed, not all PCs are competent in the same way.plus, not every fighter is tactical genius or even trained in tactics nor should it be expected for them to be.
And if there is anyone in the world who can beat someone who by all reason and logic should win it is a street thug who has climbed to the top.Our theoretical fighter could just as well be a thug who's strength attracted lesser thugs just as easily as him being actual Sun Tsu II
On Realism vs. Verisimilitude: I agree but I don't even have much to add.