I think his upside is Erik Johan Mattias "Notan" Norström
Here's the career stats to show career trajectory:
http://www.hockeydb.com/ihdb/stats/pdisplay.php?pid=3998
Mattias Norström
6'1
205 lbs
Top pairing, stay-at-home defenseman.
Matty was an incredible leader and defender. If we have a guy like that for the next 10-15 years, we're set.
I know Oiler fans won't like that comp. It's a huge disappointment given where he was rated in his youth. Larsson was widely regarded as a better prospect than Victor Hedman in Sweden, but up to this point in their development, his offensive game has just not developed. His defensive game has grown leaps and bounds over the past 2 seasons though. He will only get better.