Palermo played 3-5-2, 4-3-1-2 (one of the 3 dropping in as a CB) or variations of this system when he was there. This means he was always played as a left midfielder or wing-back rather than a full back in the traditional sense.
In that context his signing never made sense. Not even like he could have played further forward, as the wide player in a 4-2-3-1 is a very different role too.
Either he was signed without proper scouting or we wrongly thought he could adapt to a new position.