If you look at a load of breasts you'll see that there's a huge variety of shapes, sizes, profiles. Tanner stages refer to the normal basic stages of breast development in pubescent biological females. It's best to treat it as a rough guide at best. Probably every woman (trans or otherwise) has in their head a picture of the "perfect breast" they'd like to have, and most of them don't get that, and some of those that don't then get outside help approaching that "perfect breast" - it's up to the individual how content they are with what they grow. There are plenty of trans women who develop fine, "normal"-looking breasts. There are plenty of biological women who don't. It's a lottery.