But that's just smarts surely? Angelus had taken his leadership position ergo he had henchmen and Spike did not.
I doubt Angelus would play fair in that situation so why should Spike.
I always thought of Spike going to Buffy the way he did as proof that Spike was a true opportunist, that's where his smarts lay. If he saw a possibility or weakness- and he was often perceptive enough to- he would exploit it.
So he goes to Buffy when Angelus grabs Giles as hostage and makes a deal.
My point is I'm not sure Spike's smacking Angelus around the way he did is proof that he thought Angelus was the 'bigger alpha male' or anything. There are other factors.