Slaf is the furthest thing from an aggressive player, imo of course. I actually believe he's one of the softest 240lbs players I've ever watched and that's no fault of his, that's just how he's wired. If you take a look at guys like the Tkachuk's, they were bred to be physical assholes on the ice. Slaf will never be that type of player. If the team gets more physical, which is a must, I'm sure he will ramp up his level of physicality somewhat.
Going forward he can definitely learn to use his body better for shielding the puck, creating space, etc...but he'll never consistently instigate contact or violence.
He's always been this type of player