NeXT started with Display PostScript as the underlying rendering engine. The X Windows fonts require a great deal more work to be visually consistent; and are

NeXT started with Display PostScript as the underlying rendering engine. The X Windows fonts require a great deal more work to be visually consistent; and are not integrated with the coordinate system of the rest of the display. Whereas under DPS it is all one integrated method/system, making it easy to adjust the spacing between all graphical elements. I think at least, that is the reason for any visually jarring things under Etoile and this is seen in multiple Linux GUIs...