So there were two episodes that had some heartbreaking revelations about Amethyst. While it was discussed before, she really hates herself. We find out why...
While Peridot explained that Amethyst was supposed to be taller in an earlier episode, Jasper reveals that Amethyst was meant to be a Quartz warrior, the same size, strength, and abilities as Jasper. So Amethyst has been dealing with an inferiority complex all this time. In the following episode, Steven has to convince her that he sucks more because he can't even control his powers yet, and doesn't do too well of a job of it.