How and why would I become an advanced user of a program I can't figure out how to use because none of the buttons have labels?

Pixelmator Pro shows you the names of the tool buttons, once, when you first launch the app. They disappear the moment you click a button. Nice. a whole 10 seconds to memorize all two dozen of them.

And they chose not to use the system tooltip on hover, so I have to wait for some humungous pictorial tooltip to load in when all I want to know is the goddamn hotkey.

That’s rarely the case, in my experience, especially when there are a dozen monochrome icons in a row. They just aren’t distinct or memorable enough. You learn their position after a while, but confirming the correct item by their pictogram remains slower than just reading a word or two, because the words are universal, whereas the pictograms are typically specific to the application.

Keyboard shortcuts are a feature for advanced users, not pictures.