That's a fair enough point.

I'll strengthen my position this way instead. Let's assume the definition is garbage and ignore it. Are stereotyping examples things that fall into the category of sexism? I think they absolutely are. And I think most people would agree.

"Women aren't as good as men at [whatever]" - sexist? Yep "Women often have difficulty interrupting in the way that the men here did" - sexist? Sure sounds like it to me.

You're doubling down on your quick definition by pushing a simpler, even broader definition that's more trivially satisfied. This isn't an issue of categories and word use, it's an issue of history and culture and every incident is tied up in a large amount of context. This is exactly why simplifying terms and definitions fail here. It's not the land of referential transparency.

I can't say whether either of your statements are substantially sexist because they only have real meaning once you get at what underlies each one. "Women aren't as good at men at critical thinking because they're genetically programmed for motherhood while men are programmed for leadership" seems very sexist because it's talking about essential traits of men and women. "Women aren't as good at interrupting as men are because they're socialized to be deferential while men are socialized to dominate" seems not sexist because it's describing an accident of history that could as easily be the other way.

"Men aren't as good as women at multitasking" - sexist?