I haven't seen Robertson, so until then I will withhold my true/full opinion.
However initially and without prejudice, it sounds like he became a bigger human being at AZ, and thus was slowed (for the Pac 12 level) and moved to LB at U of Arizona.
Having said that, a transfer down for that type of player could do well at Safety in the FCS (where slower DB speed than the Pac 12 is required).
Regardless, I am very happy with this signing, could be a very, very big deal over the next 3 years. The Griz just got better (athletically).