When switching to the comment tab with Alt - C, I think the comment section itself is in focus and not the sample/instrument pool. Would it be possible to make a shortcut to switch between the upper and lower half? For example Tab and Shift Tab to switch between upper and lower half. When the lower half is in focus the Tab shortcut for sample vs instruments like it is now would still be working.
And maybe when you enter the sample editor via the comment tab by pressing Enter, and return to the comment tab by Alt -C that the previous state/selection is remembered? That way you don't have to reach for the mouse that much.