You have your answer.
The Stockli is stiffer and will be less forgiving of technical flaws. This makes it lousy to learn something new, but it makes it great to hone something you already know how to do, but may not master.
The SS is more forgiving and will work even if your movements are not perfect. They don't need that surgical precision that the Stockli demands, so are FAR better training skis.
Having both is a target of envy.
Cheers!