I wouldn't be so quick to write Mir off. I get the feeling Overroid has been toning down his roids to prevent being caught lately as evidenced by his shrinking body mass, whereas Mir is still full on TRT. In the battle of the synthetic monsters, Mir might be ahead!
Seriously though all Mir has to do is avoid the early onslaught. It's not that Mir is terrible, he just went up against guys with excellent cage and clinch control like Carwin, Barnett and Cormier, all top notch wrestlers. While Overeem is deadlier in the clinch with his knees, he doesn't have as good control as these guys and Mir could slip out or stalemate it, and take it to the later rounds where there is no doubt he will have the major edge.
I like this fight, it's closer than it looks. Overeem is still the safer pick but not by much.