If you use Separated Mode, you have to decide where to put the toolbar as it cannot be docked under the menubar.
You basically have two options:
• put it on top and if you save or export a document you have to drag it out of your way, because you can't read the filename. Also, you don't see all of the page ruler so you move it a little bit more down, which is even worse
• drag it to the bottom and when you click a dropdown in the contextbar, chances are good that you have to scroll down or you activate the Mac Dock...
Possible solutions:
1) don't use dialog-sheets. use proper open/save windows. at least do something with the toolbar-visibility when saving/opening/exporting
2) Of course, I have to compare it to what I'm familiar with, which is InDesign CS5:
(Yeah, I know, they did lots of messy hacks and never used the original Apple UI-elements to achieve their goals, but maybe the awesome affinity-team can do better)