How about the inconsistency of DS9 characters?
Julian Bashir was my favorite character from all of Trek, but he lost all depth when they came up with that “genetically enhanced” B.S. in later seasons. He’s just . . . he was so great at first, really human in his boyish crush on Dax and all. But then when they decided he was faking all his ineptitiude??
Just as bad is what they did with Rom.
season 1 - Odo solves a crime using this reasoning alone: “Rom is an idiot. He couldn’t fix a straw if it was bent.”
then in later years, Nog talks of his father: “My father is a genius. He could have been the chief engineer of a starship if he wanted! But no, he had to be a ‘good Ferengi’.”
ugh, not that Nog was that deep of a character to begin with, but there was a point where they decided to make half of the DS9 characters almost superhuman as a permanent plot device; that’s about when I stopped watching.