Nearly everybody in Suikoden 4 is useless, outside of the hero, Ted, Snowe and the ninja pair.
Relm with her sketch glitch fixed is pretty useless in FF6a. I really seriously only use her in the SNES game to fuck it up and give me 255 ultima weapons and paladin shields, among other random crap.
Also Peco in Breath of Fire 3. maybe there's some convoluted way to making him a good party member, but you have to babysit him to level him up any. Actually, Nina is pretty useless in that game, too, unless you can somehow transfer all of the healing spells to her.
Peco is almost by definition useless, though. You use him once to get a new master in the game and then you're never required to put him in the party again. He uses crappy weapons, so he does pretty bad attack damage. He gains status ailment spells naturally, and ailments almost never work on enemies in BoF3.
Melvin was pretty useless for me in DQ7, too. He's just not so good in overall stats and you get him relatively late in the game, without any kind of job progress on his part, while your other 3 characters up to that point are probably working on advanced jobs or have several regular jobs mastered. And I mean overall, Melvin is pretty bad in terms of stat growth. He's like second best in Wisdom and everything else is way worse.
edit: how the hell can someone hate Poo when he's the second best attacker (best if you get him the sword of kings) and all of his armor is super strong, easy to find, and protects against multiple status ailments/damage types? Plus he's the guy with a guaranteed revive and is incredibly sustainable as a healer, since he can drain PP from enemies.