Text in Writer table can be rotated via Format-Character-Position or set by Table-Properties-Text Flow or with right-click Style using predefined table style or using rotation in text box.
While this gives possibilities, it's not obvious to know nor easy to repeat.
There should be GUI option to rotate text in table.
I suggest to add 2 icons in table toolbar for rotation via Format-Character-Position and text orientation via Table-Properties-Text Flow.
I believe this would make the fans of 'many if not all functions at the sidebar' happy. My take in general: only the most often needed functions should be exposed at the UI. But lately we put everything on top...
Reading this again I see it was about the toolbar not the sidebar. But anyway, we need a UNO command that allows access to this particular attribute. And whether or not to have this in the UI is another question. Having it on the toolbar sounds reasonable, the sidebar is too cluttered right now for my taste.