I think being skeptical is fair. Even as someone who likes toughness to some degree on the roster, I have to admit that knowing how to utilize those players is a bit of a specialized (and one might say "dying") art. So, if we're making a move for players with an edge (again, not just limited to fighters here, but agitators and big hitters too), I want to feel like the coaching staff is going to use them properly, otherwise, don't bother.
That said, there might something to be said for trying a new philosophy for the 4th line simply because we can't replicate what Cullen brought now, and we don't have enough guys with hands and playmaking (even with the flashes Zohorna and Gaudreau have shown) to ice a 4th line that's capable of being that kind of line on a consistent basis. But that's Sully's call, not the front office's, and I suspect that even if Burke tries to influence it, Sully's not going to budge if he doesn't want to.