She looked good in Advent Children. And she looked like a more realistic character with sizable breasts.
Take a character like Jessica Rabbit:
It makes sense for her to have those proportions because she's a cartoon. But if for some reason you wanted Jessica to be played by a person in live action, or to have a more realistic appearance while still being animated, those boobs would naturally have to shrink a bit to fit that image. They'd look out of place on a character with a realistic face and realistic proportions.
That's what Advent Children did with Tifa. She's still maximum bust for a realistically rendered animated character. And she had a lot of life in her appearance.
The new Tifa looks dull as a character and her breasts seemed to have been redesigned not only to be smaller, but less appealing. She has pancake breasts and her shirt no longer highlights them. They've just all around presented a lesser Tifa because sex appeal is bad. But then they go and make Aeris look stunning.
