It as nothing to do with emo. It's true that the name screamo looks like scream and emo, but it's not emo with scream.
Screamo is a lot more musicaly violent than emocore.
Listen to Saetia or Circle take the square (both best screamo band), and tell me if it sound like Alexisonfire or the used. Those are emo core.. far smoother than screamo.
Saetia, Circle take the square, those are my best screamo band