I have a theory about what Steven's power really is, his power to befriend and pacify anyone. I think Steven/Rose/Pink has the power of Emotional Euphoria, the ability to make anyone feel good just by being near him.
Connie described her life as "boring and bland" before she met Steven (despite being extremely successful and competent for her age), and has dropped all interests that don't help Steven. The Diamonds were a mess without Pink, Yellow saying that they were at their worst. Spinel's rage of 6000 years of betrayal was suffocated out in 12 hours, and replaced by happiness immediately. Lars, who is supposed to be a bully, is barely even mean to Steven. Greg gave up his dream of being a world touring rockstar upon being with Rose (A dream that he ruined his relationship with his whole family to pursue). Everyone in Beach City is abstractly nice to him and understanding of all the danger that revolves around him. The Crystal Gems revolved their lives around Rose, and then Steven.
What do all of these have in common? Steven's/Pink's presence of lack of. I believe that Steven's gem is similar to heroine in a way, but for the soul. The Diamonds were barely able to operate without Pink (who was essentially a court jester), and according to yellow they thought about her every day for 5000 years. Sounds similar to a drug addict to me. When he returns they immediately succumb to him, disbanding their entire empire to please him, to make him stay. And when he does leave they follow him to Earth with intent to stay with him. Once your physically close to Steven, everything becomes ok. All those bad emotions just disappear, and you spend your days in Beach City just happy and content without ever questioning why you're so happy.
The worst part is that Steven is too innocent to understand this, and explaining it to him would essentially break his world. His power is an addictive drug that takes people in and never lets them forget how good it is.
