You're right, in that steel cases against the steel surfaces of the gun produce more friction than brass cases, and needs some type of coating to cycle reliably. Since steel cases are most often used in cheap foreign (mostly Russia and Eastern Europe) ammo where they cut corners, what coating they use often isn't very good.For me it was transition/jamming.
I don't know if I'm right, but the steel seemed to act like it looked; dry?
And locked up.
Brass was smoother.
Also, brass is a softer and more malleable metal than steel so it seals better under pressure. It should also cause less wear and tear on the gun. For AKs and other guns that are over-engineered and known for toughness, steel cases are probably fine. For more precise guns, I'd stick to brass.