Yeah, not a piece of dialogue that I'm concerned by. I'm sure that three hundred years later there are varying characterizations of an historical figure. I've even seen people argue about just how nuts Caligula was or wasn't.
Saw it again this evening and enjoyed it even more the second time. The characters, speaking of, are all great. Pegg and Cumberbatch are the standouts. Urban really isn't given much material, really, that would give him a chance to break out of that gritted-teeth-damn-I'm-irritated faux-Kelley delivery; it does get a little monotonous.