Better mouse interaction with the ruler for non touch users.
When hovering over the ruler typing numbers would let you set the rotation. It would be faster than rolling the mouse wheel for non touch users.
Alternatively you might have a hover + alt let you rotate the ruler by moving the mouse outward.
Multiple rotation speeds would also help. Maybe if oyu press CTR its fast without its like now.
A change in the Ruler UI that makes the focus more visible would also help the UI. I learned scrolling the mouse wheel works, but I had to search the internet on "How to rotate the ruler in Microsoft Whiteboard." My first thought was clicking to select, hitting CTRL or ALT, and using arrows.