That may be so, but I still get mis-gendered from time to time. The point is because i am comfortable with who I am and don't need external validation to know I'm female, I can shrug them off with a laugh. There are a few people here who I think are far far prettier than I will ever be who don't have my surety of self, who in a similar situation would possibly get flustered and defensive causing the person who (most likey) mis-gendered them completely inadvertantly, to question exactly why they got so upset and start putting pieces together and to probably read them as being male (which is the one thing they fear in the first place).
You say I look like a natal female, but even with that, if I was scared about being percieved as male then I would give myself away in the situations where people misgender me. To me, desperately needing validation is just as damaging (if not more so) as not being honest with someone about their outward appearance.