Dude this isn't the dead puck era. The Hatcher brothers, Pronger, Jackman, Regehr and those types are long gone. And reading comments like, "Yeah but how's he going to handle physical brute defenseman X?" are, well, pointless. He's either going to beat those guys with the puck and create something. Or he doesn't beat them and that's it for the play. And yes, he's going to play against an all star defenseman once in a while. But so does everybody else in the whole league. And guess what? Even those all star defensemen get beat from time to time.
DeBrincat had his detractors and he's doing great. Cole Caulfield has his detractors and that kid has looked great. f***, look at Gaudreau and Danny Briere. Brendan Gallagher, Brayden Point, Brad Marchand. Berggren is as big or bigger than all of them, can skate better than every one of them except Point, AND he's got incredible hands. This kid could be a really, really good player for us.
The SHL isn't some totally soft league. It's not as physical as the AHL (which is probably the closest thing you'll get to dead puck era hockey btw) but it's also very structured like NHL hockey, and there are games that are plenty physical. Just watch the SHL playoffs. He did plenty fine against physical defensemen in the SHL and even threw a few shots Seider's way.
My advice is to just wait, watch, and see. If Berggren has a fiery competitive spirit then he's going to be just fine.