I've played every FF out there (save for the ones unreleased in America at present) and I think Tifa, Lulu, and Yuna are some of the best characters of the series. Although none are my very favorites, Tifa is an amazing character and a great fighter. She's kind, reliable, and sweet. She cares more for Cloud than for herself, and without her he never would have uncovered his past and come to terms with himself.

I fail to see how any of them (save for perhaps Lulu) is uneeded.

To me the posters anger over these three seems like a Mary Sue obsession with the men these three are associated with, rather than a problem with the characters themselves.