It proved that children’s media could handle trauma without being grim. It showed a gay relationship (Ruby/Sapphire) as the most stable, heroic thing in the universe—not a "lesson" or "special episode," but the literal engine of the plot.
"They're my family." Steven looked at his gem, glowing faintly in the rearview mirror. "I'm not a Crystal Gem. I'm not a half-Gem. I'm just Steven. And I don't leave my family behind." Steven Universe - Season 1
Season 1 introduces fusion (two Gems combining into one being) as a visual metaphor for relationships. The season draws a crucial distinction between healthy and unhealthy fusion. It proved that children’s media could handle trauma