From his core, Madara is a broken character. Makes no sense, is cliche and not in a fun way, I always yawned when I say him in the manga. Dullest Uchiha by far.
Obito (restricted from Kamui-ing Jin's in their sleep)
Kisame (restricted in his first battle with team Gai, and forced to lose against 8 tails and Samehada betrayed him)
if you mean broken character then that goes to Sakura, i dont think she is even a character at all but as a joke through out of the series. That broken character has to be removed or replaced with something else. You dont write a main heroine to become a pathetic hoe that completely opposite to the ideal woman with pride and equality.
Nearly everybody in this series could have been broken. Evidence of this could be seen in the old Ultimate Ninja game series on PS2. That's why the giant nerf took effect in Part 2 as for Kishi not to have to write characters to their fullest potential of power. Then if not that nerf certain characters reputations in power or title as exemplified in most the Hokages.
Itachi. That guy was ridiculously good at everything he did.
Shisui, the fastest uchiha beaten by danzo of all people.
Kabuto, asspulled by izanami
Obito, didnt use any large scale mokuton, barely used any rinnigan powers or sharingan power
Tobirama, reduce to a sacrificial pawn against no names