The problem isn't that margins should have a specific size but that the design as a whole should feel cohesive. It's the balance of padding, margin, font sizes, and text alignment that is all wrong. Not just one specific thing, but the whole thing. Nothing lines up vertically. There are too many and too few borders. Some invisible borders take up space and others don't.

Big margins and tons of whitespace is fashionable. Good design doesn't need to be fashionable, but it does need internal consistency. A Mac-style dock with big rounded corners needs some space to breathe. If you don't want to sacrifice that screen space then maybe it's better to go for a more angular design.