Rikku was not changed/censored in any significant way. So honestly I think someone at SE is the one who drew Rydia with that new dress on and sent it to them as the reference. They didn't send them any Amano art/sprite art or the CGI art from TAY of Rydia. They paid some random guy to whip up a new Rydia design and that's what the artists were sent as reference material.

Otherwise, why would multiple different artists draw Rydia with the exact same frumpy dress on, whenever every other FF character has a much more faithful depiction