He's got one advantage that all the other Gems, even the Crystal Gems don't really have.
Rose had it to an extent and she saw it in humans, how one human can make another human open up to them and change them with Kindness. She understood that only a creature with the emotional range of a human (Enough) with the power of a Gem could really take on homeworld, since its something they have no defense against.
Homeworld is all about STRONK SURVIVE, WEAK SERVE. Even the Crystal Gems resort to violence before any other potential answer.
Steven doesn't. And that's the reason he got through to Lapis, then Peridot. It'll be how he gets Jasper eventually. What can the Diamonds do against that really? Continue beatings until Moral improves?
The only way they'd survive is to change their entire social structure, which won't happen because the Diamonds won't comprehend what's happening until its too late, they won't realize the soft power of Kindness.
Rose created the Gemworld equivalent of a Biological weapon, a virus that infects anyone it touches and turns them into a carrier, bringing it to anyone they come into contact with bar a few immune creatures (The ruling class that have nothing to gain from being treated kindly)
Rose Quartz has weaponized compassion and Steven is the delivery mechanism.