Meh.
He clearly comes into fights with an established perspective of each fighter and what they ought to do. He then follows that template in his commentary, even when the fight plays out differently. And he emphasizes the things he thinks each fighter should be doing, even if they aren't doing so effectively or very often.
So yeah, he is biased in that sense fairly often. But I think he is rarely biased in the sense of preferring one fighter to the other.
On the same point, I have often witnessed the phenomenon in other sports where fans are so biased that they accuse relatively objective commentators of being biased for not seeing everything one way. I'm not sure if that is at play here, but in some of the anti-Rogan threads that pop up after cards you can see it.