As for months/years or training - sure, there maybe (or maybe not even training in the tool per se, but more like general education; you need to know what the data shown actually means). But in a typical tool, 10 seconds or even 5 minutes of training won't kill anyone and would vastly improve efficiency. Want a proof? Video games. Each one has a custom, specific UI. RTS games have so many stuff on screen that they often have tutorials and in-game help. And 8-year-olds have zero problems with understanding all that in under 5 minutes. Outside of gamedev, people seem to have forgotten the concept of introduction, tips and tutorials.
Please backtrack a minute: What we're trying to debunk is that "Whitespace is always bad". The rant you're going into, here, is that some tools are oversimplified or don't give you immediate access to functions you need. That's the tool not doing its job - it's bad UX. Nobody will argue against that.
It also has nothing to do with whitespace.
> Outside of gamedev, people seem to have forgotten the concept of introduction, tips and tutorials.
SMB 1-1 is often praised as having outstanding video game level design. One of the reasons is exactly because it doesn't use "tips and tutorials". It intuitively teaches you to run towards the right, to jump, how to kill enemies and discover secrets without ever popping a tooltip on the screen. Not that those are always bad, mind you, but intuitiveness is game design by excellence.