I have a slightly differing take. Pre and post draft I've always been somewhat impressed by Carlsson' s relative strength with possession of the puck given his frame. In the SHL and the WC he was a lot harder to knock off the puck than you'd expect from a guy his age with his frame. That became less of a factor in the NHL as bigger and stronger guys were knocking him off his skates but he still has a fair number of moments where he can keep his balance and possession under physical pressure.One difference for me between Carlsson and Sennecke is that, despite being a twig, Beckett already seems confident and willing to throw his body around.
The worry I have with Leo is that, even if he fills out, convincing him to be physical might be like convincing Getz to shoot more. I just think it's hard to get a player to think that way when they're already 23/24.
That said I don't think he needs to be a very physical player to be successful, just a little bit might go a long way for him.