As the ESPN article points out, trimming down was absolutely key for players like Martina and Lindsay Davenport to reach their potential...but to have the kind of feedback Townsend has had would have been devastating to them at the age Townsend is.
Clearly, given that she's the top-ranked juniors player, she's tracking just fine relative to her peers. If she's competing in the WTA and isn't winning matches she should because of movement or just tapping out physically/mentally in three-setters, that's when she, as an adult and a professional, can make a decision about her weight and how great she wants to be.
I will say that Serena, among others, has implied that some portion of the USTA's position is racially insensitive (i.e., many Black women tend to have thicker body types). Lord knows, tennis as a sport is not one that has historically been racially inclusive, but in fairness, Taylor is legitmately heavy. Sloane Stephens, and Serena herself for that matter, are two examples of Black women who have thicker, but nevertheless extremely fit, body types. Not defending the USTA's handling of this overall; I'm just saying I don't think it's racial.