Extend a Layers timing: Timeline vs Xsheet

I want to extend all layers at once by 10 frames. In the video link, I show several ways I thought it could be done.
It is not intuitive that the “Extend” command behaves differently in the Xsheet vs the Timeline.

Finally what worked was selecting every layers cell in the timeline.
I would like to request that timeline have a “Select column” similar to how I can select a row in the Xsheet.

3min video demonstrating inconsistancy: