I don't know about not pivoting, but I agree Sergio's footwork clearly was not the best, he got his own feet mixed up a lot and his foot positioning didn't line up with where he'd be placing his head so he'd put himself off balance and would sometimes get punished for it, but, he could move his feet really really really quickly, had an awkward style and threw a good jab with very fast hands and had incredible reflexes.
Also don't personally think Sergio would start fast or do well being aggressive, Canelo would catch him too often. He'd have best odds just moving laterally a lot and trying to get Canelo to come after him. Sergio's fast feet should see him make the 12 imo with enough power and speed to keep Canelo honest and take some rounds, Canelo's not all that scary when he has to come forward unless he's in with C level guys.