Who wins is always going to be decided in an unfair manner, by the writer.
What makes good writing is convincing the audience that the victory actually makes sense and is good for the story as a whole.
This is why just saying "I'm the author, so it makes sense because I say it does" is also stupid. If you're going to break your own universe to satisfy your personal agendas for characters, you're a bad writer, at least as far as most people are concerned.
Power scaling a series like One Piece properly is almost impossible, what matters is that fights are either fun; informative; have emotional stakes; or change the world. Does Luffy beating Crocodile, then having Croc clash with Mihawk and Akainu really make sense? No, but, fuck, it was hype, so I'll allow it.