The problem is if it isn't a dedicated video app. Say for example a video embedded in a webpage. Then you can maximise the browser window, but the video itself still takes up a small part of the screen.

> And if you want to see other apps at the same time as the video, no wonder full-screen gets in the way.

You say that, but is doesn't on windows or linux. And it didn't used to on macOS either until they changed things around a few years ago.