When Dougie Hamilton sustained his left pectoral muscle tear last November, quite a few fans felt that it was going to be a "blessing in disguise." His lackadaisical defensive effort sometimes resulted in the Devils surrendering odd-man rushes and open breakaways. However, as the season progressed, people realized how imperative Hamilton was on the Devils' roster. I would go as far to say that the Devils' defense got worse. While Hamilton wasn't the best defensive player, his impact and contribution were still dearly missed.
Power Play Struggles
Even though Hamilton was placed on the second power-play unit, he was still a big contributor. Due to his wicked slapshot, Hamilton was able to create better scoring chances for himself and others. He is also a much better shooter than Luke Hughes and Simon Nemec. Unsurprisingly, half of Hamilton's 16 points came via the man advantage (four goals, four assists).
When Hamilton was healthy (October 12 - November 28), the Devils had the best power play percentage in the NHL at a 36.8% clip. After his injury, the Devils only converted 17.1% of their power play chances for the rest of the season. While he wasn't the sole reason for that decline, he certainly played a big factor.
Not Much Assistance or Depth
Once it was determined that Hamilton was projected to miss extended time, Nemec was given the nod to fill the void. While he and Hughes had their moments on the offensive end, it's clear that they still have a lot of work to do. Especially toward the end of the season when they both seemed fatigued at times. Hamilton would've collected a decent amount of those minutes and kept the defense more "balanced."
Hamilton arguably has one of the best slap shots in the entire NHL. Even if he doesn't score while unwinding from the point, he still creates a decent amount of chances in front of the net as previously mentioned. That's where players like Timo Meier and Dawson Mercer thrive: collecting the loose change in front. Either way, Hamilton would walk away with a point. Bill Spaulding and Ken Daneyko acknowledged that Hamilton's absence might've played a part in Mercer's points dip. Despite Hamilton's defensive struggles, the Devils didn't exactly improve when he went down with his injury.
Hamilton is entering year four of his seven-year deal. When healthy, he has proven himself to be a vital asset on the Devils roster, as shown when he played in all 82 games last season and tied Barry Beck's franchise record for most goals by a defenseman in a single season (22). His only goal in last year's playoffs saved the Devils season. It was the game-winning goal in overtime to make sure that the Devils didn't go down 3-0 against the New York Rangers at Madison Square Garden.