I really dont know wtf you're talking about, the only reason Yuffie is "weak" is because when you recruit her she's a couple lvls lower than your party. Level her up a bit and she does just as much damage as anyone else. Yuffie's limits were fine too. If you wanna talk about shit limit breaks then look at Tifa, Cait Sith, or Vincent. Vincent's is actually semi-useful since it doubles his HP, but it sucks not being able to control him.
Most useful limit breaks though...were those of Cloud and Barret.
When do you recruit Yuffie? I tend to get her as soon as I am on my way to Junon (Which is the first time you can actually recruit Yuffie) and she is normally my second/Third highest leveled character. Once she was even higher than Cloud when I got out of Midgar at about level 15.
Anyway, I kind of like Yuffie. I always liked her in the game but when I saw Advent Children, I suddenly grew a bit of dislike to her as I just thought she was an annoying little bitch but in the actual game, I do like her. She usually remains in my party until I get Cid (That's if I didn't get Vincent before Cid but I usually do).