He's super aggressive at meeting puck carriers in the NZ and using his stick to disrupt rushes. Also, stepping up to keep cycles alive in the offensive zone. That's partly his version of being aggressive and where he creates his edges.
I assume he spends less time in the defensive zone than most because he makes it difficult for the opposing team to get there in the first place. He's hell to get past in the neutral zone and blue line.
But yes, his 50/50 battles down low could improve. Seemingly, he mostly chooses to pin the opponent against the boards and then wait for help. I think Sanheim does probably get to a lot of pucks first and moves it quickly, though. Leading to probably less conventional battles than a lot of other defensemen.
He's 10th in GAR and 12th in WAR amongst defensemen in the NHL.
Just doing a little digging. Sanheim seems to rate well in ixG, and other individual metrics like iCF and iHDCF. I don't know the formula they use for WAR or GAR, but maybe those individual stats are given heavy weight?