I dont see why he would struggle. Lacy was all over Calaghe. Theres no way Clazghe is keeping Benavidez off of him. I doubt he can knock him out. Calzaghes head to head ability is very overrated because he was undefeated. He wasnt that dominant in reality.
You have an arguable point that Benavidez might walk Calzaghe down, but saying Calzaghe wasn't a slick boxer? That's just not true