Robbed is probably a bit of an overstatement. Although, I think Hendricks really controlled the match but Lawler came closer to ever finishing it.
I am a Henderson fan so I don't love Pettis, but I agree that he's a great fighter. He and Jon Jones are probably the two most dynamic strikers in MMA, although Pettis is flashier whereas Jones just picks people apart, brutally. Pettis also has great submissions, hence his catching Henderson, a BJJ black belt.
I don't necessarily agree that Pettis is the single best offensive fighter. I think he is probably the most gifted offensive striker, but Chris Weidman and Rhonda Rousey are both incredible offensive fighters, but their offensive grapplers. In general I would agree he is in the top tier of offensive mma fighters with Weidman and Rousey.