Here's how you actually should look at that series because it's closer to the truth. They were indeed grossly outmatched, as was evident by the possession and shot generation advantage in favor of the rangers for the majority of the series. Highlighting the goal differential in each of the losses without context is the biggest fallacy to come out of that series when attempting to take something positive away from it, which there wasn't much.
For the most part, the rangers played a much faster, counter-attacking style during the regular season compared to what they displayed in the playoff series against the pens. The two primary reasons for this were simple. Johnston (in what was in no way a stroke of coaching genius, how to trap is coaching 101) altered his system to about as conservative a trap as possible after the injuries to the majority of their competent puck-moving defensemen (because his junior tier system completely relies on these types of players to even work), which Vigneault cleverly countered by taking what the pens were giving them without overextending, resigning to play as safe as Johnston had the pens playing while still guaranteeing they would eventually grind out enough wins to move on because of their superior speed and physicality, no matter how close the final boxscores were.
A crippling flaw in the pens roster/Johnston's system was obvious for most of the year actually, against the rangers, isles and capitals especially, which contributed in large part to their pathetic divisional record.