Do you understand what "sexism" means? Would you recognise it? Because you've just given a great example. To say that a word is gendered is not the same thing as saying that role is gendered. The vast majority of brick-layers may be male, so the role is gendered. But the word "brick-layer" is not gendered. However, your example of "chairman" clearly is a gendered word, as it automatically makes anyone holding that post a man. Which is why the word used these days is usually just "chair" (I'll agree that "chairperson" is clunking, but blame it on the English language). Women quite rightly object to using the word "chairman" when the person concerned is female. But it means that you need a word which is either not gendered (like "chair") or a special word for the female version ("chairwoman"). You need no such linguistic silliness for "superhero", which is perfectly adequate to describe Wonderwoman and Superman. The fact that the majority of superheros are male is a completely different sexist issue.