While I agree with you on principle, there's a nuance here that needs discussing.
I'd amend the 'best defense is offense' mantra to 'the best defense is puck possession' which you kind of allude to. In that vein I'm reminded of the many times Bryan Campbell, who by acclimation 'wasn't that great defensively,' bailed us out in the defensive zone by getting his hands on loose pucks or by receiving passes in tight coverage just to dipsy-doodlee his way out of danger until he could pass the puck up through the neutral zone. He was so incredibly valuable in that regard.
But with that being said, if you don't have skaters - both on defense and at forward - who are able to force turnovers down low with hustle and positioning then you're just asking for your opponent to hang onto the puck until they have a high-danger chance. You can't have possession of the puck all the time, that's just a fact. That's why guys like Slavin, for example, are so valuable when they're on the ice. He's second to none at timing his move and disrupting the play with body and stick.
My point is that you're right, puck possession means everything, but during the 45% of time or so that we don't have the puck we absolutely need guys who can either help force turnovers or disrupt would-be high-danger chances. I generally like where our roster is going but I am concerned that we're somewhat lacking in that category.