Just my thoughts. But then you would loose your header text etc. I think this is a minimum width of a column. You have the icon of the column type, the column name and the dropdown widget to edit the column. You can see when you move your mousepointer from the left towards the triangle of the dropdown widget that the triangle changes color when you are a number of pixels away from the widget.
Maybe that margin could be made smaller. Or maybe we could get the option not to display the icon of the column type. This way columns could be less wide.
Another idea to make it less wide would be if for instance the dropdown menu becomes available when you press the right mouse button. So you wouldn’t need the widget in the column header.