If they are all the same because of the blonde hair, it means that both of them are dumb and that I, being Asian, are therefore the same as another Asian that is Korean. Don't subjugate me to that kind of prejudice. This generalization is overly simplistic and somewhat childish, but be that as it may...

Rinoa is in no way similar to Garnet or Lulu, except haircolor, which is a baseless facade considering that they came form the same character developer AND that there's only so many colors of natural hair in the world. Cloud != Tidus nor Shuy-- well, maybe he == Shuyin, but not Tidus.

Emo & tempermental != Optimism and cry-baby-ish-ness

Anyways, back on topic, besides having themselves in KHII, they don't really have alot of similarities to characters that come after them; well, at least until I play FFXII. You could also say that Yuna heavily influenced the female main in FFXIII, (concept of female independence and hairstyle) but since not much has been revealed about her, except for a statement by Nomura that states that she is essentially a female version of Cloud, you can't really come to a very stable assumption or comparison.