I agree with what you are saying to an extent. But it does come down to what should be normalized and what will remain an outlier.
Should a female founder be considered a permanent outlier? Probably not. There is nothing intrinsic about an female that makes the pre-disposed to *not* being a founder. The addition of outlier status is a continued identification of it being unique, different. What percentage of female founders does it suddenly not become rare - 1%, 5%, 15%, 30%? I dunno, but if a woman who is a founder is called often called a "female founder", and a founder who is male is rarely called a "male founder", then there is something wrong. I can't find a reference now, but there is a CEO who tells a story about how she always gets a cup of tea as she walks into a high power meetings with CEOs, etc. Her initial read of the room is if she is asked to "hey, can you get me a cup as well?". Those questions are rarely asked of males.
Should a white fox with red eyes, or a (as you put it) "a woman with three tits" be considered an permanent outlier - yes - absolutely. The difference is an intrinsic different that is an outlier only within the context of that individual. It is unique, always will be unique. If for some reason, white foxes become common (I think arctic foxes fit that), then you have particular names prefixed for that reason - Red Fox. Arctic fox. Gray fox. are all specific types of fox, and when talking about foxes you will generally include the type - or rely on the local type as the norm.
More broadly, and more ironically, insisting on calling women who are founders as "female founders" is continuing a stereotype that "founders" are generally male, which makes the biases and behaviors of the founder community negative and potentially psychologically aggressive to female founders.