The thing that made SunTour better was the slant-pantigraph design for which they held the patent. The slant followed the contour of the cogs, keeping the jockey pulley a constant distance from the cog for faster more consistent shifts. When the patent ran out, Shimano jumped in with a flock of better working slant panti derailers. Suntour went from the top to insolvency just over a decade later.
Kevin Casey
Championship Wheels
Encino Cyclery