> I don’t know what you gain other than oh-that’s-not-google-slides brownie points.

Well, there's at least better version control with git, and the other general benefits of plain text. If you have a bunch of presentations, easier to search among them based on content if they're plain text.

Though, presentations being presentations, the fact that they generally lack content to be useful on their own without their presenter, makes them kind of disposable as documents.