Oh, no, that’s not at all what I meant!

Powers are nifty, but they aren’t really important to the gems as characters, with a few exceptions.  Stevonnie not showing off any abilities other than what Steven and Connie bring to the table doesn’t matter to me; what matters to me is that they’re just...Steven and Connie.

Garnet has unique traits inherent to her  that are not part of Ruby or Sapphire.  So does Sardonyx, so does Sugilite, so does Malachite.  As far as we can tell, so does Opal.  These gems are their own characters with their own wants, needs, and desires that largely but not entirely line up with their component personalities.  When I say multiplicative, that is what I mean.  Garnet wants things and interacts with the world in ways that are not Ruby+Sapphire, but are the unique perspective and personality of their union.  It’s like if a married couple were having an argument and the marriage itself chimed in to give its opinion.