I can kind of see where the OP is coming from because. Well for starters, an established character is someone who you can identify, know, and has a place within the story. I have a hard time justifying a gender flip due to certain things not matching up when it’s done. Genderbend is a common practice but for the most part it could come off, what’s the word, “Inconsistent.”
To successfully genderbend a character you must keep all their preferences, likes, dislikes, and overall appearance except for the gender part mostly the same.
Imagine an iconic character like Goku per say, and make him a female saiyan. That’d change… well a LOT of things. First off, Gohan wouldn’t exist. That’s a plothole. Second off many things in the story would change. Encounter with Bulma is one of them.
I also feel like the character’s personality is undermined. Having no official gender or background makes them seem like someone who is a character depending on how you interact or perceive them. While that CAN please the reader, it will certainly take creative freedom away from the author as scenarios they had in mind becomes impossible due to having to find a “gender neutral” agreement.
Just my 2 cents.