They can project all they want, and I'm sure there was supposed to be some comparison with transgender stuff, but logically speaking, Steven is more or less Pink Diamond/Rose's son, not her. Granted, it's all framed in a subtle enough way that fans can say, "See, it's transgender symbolism!" And Rebecca Sugar (the show's creator) can say, "Uh, yeah, sure, that's what I intended!" when the truth is more likely that she was not immediately thinking of the supposed symbolism at the time. Despite transgender stuff being seen as the "final frontier" for the show and the show's infamous LGBT/SJW symbolism, if they really want to be explicit than Steven would have transformed into his own mother, rather than remaining himself. If anything, Steven remaining himself helps him assert his own identity as an entity descended from but also separate from Pink/Rose.