I'm a researcher in ML security.

I also have five years experience in music copyright and royalties. I still know stuff about weird esoteric distribution policies PRS for Music has, like the Educational Recording Agreement or how the pubs and clubs scheme analogous apportionment of £40 million worked.

Then there's the digital signals synthesis techniques I've had to learn in the last two years as well. Literally building bare bones software based synthesisers.

And then there's all the ML stuff and the security stuff...

So I wholeheartedly disagree with your definition. Knowledge is often much fuzzier than person is working on X, therefore they must only know about X.

A stamp collector, by definition, is someone who spends all of their time collecting stamps, so they would have no time remaining to get operational experience.

that's just silly. someone with operational experience can switch to ai research later in their career. probably not super common, but nothing definitionally wrong with it

There is applied science.

They probably have experience of using e-commerce though.