It would be great to have a more robust column width behavior in the style panel for the Builder created Column Element.
Setting "n minus 1" columns at fixed px size, with the remaining one as auto, is a very common use case especially in tables. You typically want a few things fixed at left or right (such as action and indicator icons on rows and the like), and a "main" column that stretches to max available width of viewport.
You can set the width of a column element in the JSON view but only has a percentage. It would be great to have more robust editing.