I built a new version of Sigil with the last commit and... it's great!
Indeed, these five main sub-windows are the most important elements of Sigil's interface, the ones we navigate most often. Once you've assigned keyboard shortcuts, you can get used to it very quickly, and it's especially important that you can 'escape' from CodeView, which most often took 'control' of the cursor.
VERY much!
As I use Sigil practically every day, I have become accustomed to its minor imperfections. That's why I usually read every post in the Sigil section on MR carefully, because often fresh users can articulate their needs better and suddenly it turns out that it can be even better!
Such easy jumping between windows is a real convenience for me to work without taking my hand off the keyboard.