Regarding the Bergeron comparision, one thing I'd note is that Bergeron wasn't really expected to win any Selke trophies himself when he was Rakell's age, at least as far as I can remember. That came a lot later. To me, elite defensive ability is one of the most difficult things to project. It just comes to some guys over time.
That said, I'm not really seeing the Bergeron comparision, other than being a two-way player. Both up front and defensively, respectivey, I can't really see Bergeron as too similar. I'm really excited about Rakell, nonetheless.