[zozbot234]

Information hierarchy is relative. You can totally allow for it within a denser layout, in fact traditional dense GUI's and text layouts pay a lot of attention to proper hierarchy. Where whitespace seems to be inescapable is for separating active elements of a layout, to avoid unintended touches.

[senttoschool]

You should try UI design. Open Sketch or Figma. Start putting buttons and boxes together. You'll quickly realize that having adequate spacing is absolutely a must. Everything just looks awful without enough spacing.

Usually, the biggest problem a piece of software has is adoption. People are far less likely to adopt your software if the first time they look at it, it looks like a huge complex mess. The sales people certainly won't want to present software like that to potential customers.