The difference is that Arno and The Mandarin are both very different takes on what an evil Iron Man IS
The Mandarin is the hypermasculinity inherent in the very name "Iron Man". He's an imperialist, a bloodthirsty martial artist, and a banger of harems. He is yang-chi made flesh.
Arno is the coldness inherent in the name "Iron Man". He's coldly utilitarian and full of hubris. He wants to solve all the chaos of the world like it was all an interesting equation, and does not care about any individuals who die along the way.
Very different villains, yet both are evil Tony Starks, embodying his worst traits with none of his empathy.
If this theory is true, then what we will see is a war between Tony Stark the hypermasculine conqueror and Tony Stark the cold utilitarian, with the real Tony probably coming back at the end.