I don't really see it. Shields is nowhere near the athlete Pierce is. Pierce has never been a guy who put much work in developing his body and has always looked soft, but I'd say he's an elite-type athlete naturally.
Shields is a Ryan Anderson or Brandon Ubel-type athlete. Not very quick, doesn't have much of a vertical, not explosive at all.
In terms of ball-handling, that is also not a strong comparison. Right now I'd say Shields is a pretty poor ball handler at his size. Reminds me a bit of Toney McCray in that he just looks a little scary when he dribbles it too much. Pierce was and is an excellent ball handler for a player of his size...again, probably an elite-type ball handler in comparison to Shields.
That being said, I like Shields and think he can end up being a decent player (solid starter, but not an all-conference type)...but when it comes to comparing him to Pierce, I don't see it.