A really solid mid-range game is a scarce commodity in the league. Aldridge has a solid mid-range game. He also gets a lot of put-backs, because he's playing close enough to the basket, which he would not get if he was out on the 3P line.
He's shot around .700 from inside 3 feet, and still well above .400 all the way out to 16 feet. (This year, he's shooting .427 from 10 feet out to the 3P line.) I think it's pretty clear that he could knock down a decent percentage, if that was a focus. But there are guys who can sit out on the arc and make 3's. Not too many guys who can do what he does close to the basket. Having LMA out there would be giving up too much that can't be replaced.