Well, most of Tiptree’s stories that don’t fit into that (and that’s a pretty superficial description of “Houston, Houston,” which was a new twist on the idea of life with just a single sex). In addition, “Houston Houston” came out just about the time her identity was revealed and a year after Silverberg wrote his introduction, meaning that the suspicions preceded the story.
The question came up not with that, but with Tiptree’s 1973 story “The Women Men Don’t See,” which portrayed women quite realistically.
Tiptree first made her reputation with “The Last Flight of Dr. Ain,” still one of the best SF stories ever. What is absolutely stunning about the story is that she take a very innocuous sentence and, in context, makes it one of the most horrifying thing you’ve ever read. It also, in hindsight, seemed to predict AIDS (though a much more virulent form of it). But it is not a feminist story by any means.
Other great Tiptree stories include “And I Awoke to Find Me Here on the Cold Hill’s Side,” “The Man Who Walked Home,” “Forever to a Hudson’s Bay Blanket,” “Love is the Plan, the Plan is Death,” “The Girl Who Was Plugged In,” “The Screwfly Solution,” “Time-Sharing Angel,” “We Who Stole the Dream,” “Backward, Turn Backward” (actually a reworking of “Hudson’s Bay Blanket” with a nice take on time paradoxes) and one of her posthumous stories (I think it was “In Midst of Life”) that is the creepiest story ever written (if you know about how Tiptree died*).
In any case, other that “Houston, Houston,” and “Women Men Don’t See,” the rest of her output did not have any particularly feminist bent.
*Tiptree committed suicide by shooting herself after killing her ill husband. The story portrays a person shooting himself and ending up in a wonderful afterlife. :dubious: