Makes sense, in a way that inefficient T and especially DHT suppression is guaranteed to stall or limit breast development. Also there's a stydu on young trans girls taking Bica as a puberty blocker which has on its own resulted in quite subtancial breast development. But to say that estradiol levels have nothing to do with it is likely false, it does, but what is the perfect balance is genetic and individual thing as there's a whole lot of difference on that.
For example, how did I experience a massively accelerated breast develpment after all this time when I started taking higher dose of estradiol? It feels like the change was about getting the balance right. Ton of factors in play but the correlation is obvious and I can track it down to days from making that change.
I think this study is correct in the finding that testosterone suppression is key to maximising breast development. But its not something that wasn't already widely understood, or at least shouold be. It says a thing about priorities for ensuring boobie fairy being happy. Balance, getting rid of the things that obviously suppress breat development.