I agree about the voting.
I think the most important thing is that the buttons are consistent in their category and that we don’t have too much categories. All app dialogs should have the same button and all shell dialogs should have the same button, but I don’t see an issue in having big differences between app and shell dialog buttons, as long as it makes sense: all UI elements of shell are flat, for example, so it makes sense to also have shell buttons be flat. Most app elements have some depth in them, so it makes sense for all app buttons to also have some depth in them. The header bar, being something in-between, is thus semi-flat…?
I’m not really proposing anything, I’m just saying that I think it’s ok to have big differences between categories, as long as it’s consistently applied to everything in the category and as long as there aren’t too much categories.?