Here's the thing... Steven should have been like her mother. From the start, he was whining about "MUH! I CAN'T DO ANYTHING AS MY MOTHER DID!" He did everything he could to perfection his battle skills, and once the gems invaded, he only did was to talk to them... and redeem them, all that training and for nothing! All he did was talk! We wanted to see his full potential, not him just talking. He should have stick to his gun and fight back!
While Star only did it for one reason... human dick! And the only way to do it was to eliminate everything that's magic and to dispell all those armored giants. But in the end...she killed everyone that's magic! and fused her world with the earth...just for cock!
NOW YOU SEE THE DIFFERENCE!