There's no defending it lol, One Piece is a battle shonen. Fights are the single most important thing in this manga whether people want to cope about it or not. Luffy is not defeating opponents or freeing nations by sitting down and having political discussions. Every problem is solved by Luffy kicking someones ass. He should have picked a different genre if he wanted to ignore having any sort of logic in fights.
But this goes beyond giving him freedom to draw whatever, I understand Oda won't fully explain haki because it gives him breathing room to make shit up as he goes. Issue is he introduced many forms of haki already but failed to visually distinguish them. There is no telling wtf Luffy is using half the time. This is him failing as a mangaka, this is a visual medium.