1) Kimimaro. He was hyped up and really seemed like a fierce opponent... but was beaten by a part 1 drunken Lee. I know he was ill and all and also around 13 too, but come the hell on. A hyped up KKG user against a drunk kid with only taijutsu at his disposal?? Nope. #1 failure of a clansmen/KKG wielder.
2) Obito. Yes, I know his Kamui is one of the best abilities in the whole series as far as it's uses and had he had both eyes at the same time.. it would be even more OP.. but he might not even have awakened the MS had Rin not died the way she did or at all. If Madara didn't ever step in he would have been just a regular fodder Uchiha by the time he's an adult. (There were a lot of them that weren't mentioned or hyped...sooo I guess quite a few Uchiha fall under this as well?)
3)Mei. She was underwhelming, but maybe it's because she wasn't a main cast member?
4) Shin. Both child clone and the original. Potential was wasted. Only took Sasuke, Naruto, Sakura, and Sarada to stop them because of plot alone. I'm pretty sure Sasuke or Naruto on their own (esp together) could stop them. Not the highest on the list because they did put up a decent fight considering plot was nerfing them.
5) I'm not too sure who to put here. I could say Hinata considering she's a main family member and daughter of the clan leader.. but at the same time is she really any more fodder than other members, or just didn't live up to her father, uncle, Neji, and Hanabi's hype? We don't hear of other Hyuga being exceptional or above average in their clan.. so for her main family (the ones I listed) yes she makes the list, as far as her whole clan though? That's debatable.