It's always tricky to project an NHLer's impact with a new team before he has a chance to suit up and take to the ice in a game setting.
That being said, Jeff Petry's qualities fill an important gap for the Habs and can help put Montreal over the top heading into the business end of the season.
Who is Petry?
The 27-year-old native of Ann Arbor, Michigan, son of fomer MLB pitcher Dan Petry, was drafted in the second round (45th overall) by the Edmonton Oilers in 2006. Making the jump from Michigan State of the NCAA to the pro game in 2010, Petry had a short but successful apprenticeship in the Oilers' minor league system, tallying 28 points in just 51 AHL games.
Though Petry does not possess the top-end skill of another right-handed defenseman plucked in the second round currently playing in Montreal (that would be P.K. Subban) the speed of Petry's development mirrored that of the former Norris Trophy winner. By age 24, Petry was already driving the play and taking on top-pairing duties for an Edmonton team in the midst of an anything-but-pain-free rebuild.
Consider the Deployment Chart of Oilers defensemen (min. 800 5vs5 minutes played per season) since 2010:
Going by the chart, it would appear that a prime Tom Gilbert, back in 2010-11, was the closest thing the malaise-era Oilers had in terms of a number-one defenseman. Petry did well enough in terms of driving puck possession, considering he consistently played more, in tougher zone starts and against stronger competition. But he was never going to single-handedly turn Edmonton from a lottery team into something more, the way Subban or Mark Giordano can.
In a way, Petry is the victim of the dreaded "Patrice Brisebois Syndrome," criticized for playing above his pay grade on a really uncompetitive roster. If you're good, but not great, playing top minutes for a bad (Canadian) team, people tend to thing you are worse than you actually are. Phil Kessel and Nazem Kadri on the Leafs are some other examples of the phenomenon.
Where does Petry slot in?
The best possible news here is that, in Montreal, Jeff Petry will not be expected to carry the flag to the same extent he's been forced to in the Prairies. Joining forces with Subban, Markov, Beaulieu, Gilbert and Gonchar, the American will give the Habs an ability to ice three NHL-proven puck-moving pairings, which would be a first in pretty much forever. Looking at a few HERO charts will give us a rough idea of where Petry stands compared to some of his new teammates:
Legitimate #1 defenseman in every way, a generational talent.
Markov: Still a top-4 defenseman, but his age is catching up with him. We could reasonably assume that Subban is carrying him a little bit.
Gonchar: Imagine Markov a few years older, and not playing with an All-Star. Not pretty. However, he's been serviceable alongside Beaulieu (who did not play enough minutes to get his own HERO chart.
Gilbert: Still a solid top-4 blueliner who can put up some points and move the puck. On the one hand, he has a strong track record and is definitely better than his Habs tenure has been so far. On the other hand, I would caution that he is indeed slowing down, having turned 32 last month. He also had a monster season last year in Florida playing with Brian Campbell, a guy who help almost any NHLer put up a great Corsi rating.
Petry: A similar player to Gilbert, except with a lower Points/60 and more ice time. Considering he played on some truly brutal Oilers teams, even his Usage Adjusted metrics (UA CF/CA & UA FF/FA) could be selling his abilities short.
What's the upshot?
In sum, Jeff Petry's arrival makes everyone on the Habs' blueline better. Markov-Subban will no longer need to play over 27 minutes per game, which will allow them to feel fresher heading into the post-season. Beaulieu-Gilbert will no longer need to start as many shifts in their end, which will allow them to use their vision and passing skills to put up goals on the board. As for Gonchar, Emelin or Weaver, they'll get to play with someone who has consistently managed to float replacement-level players such as Andrew Ference, Theo Peckham and Ladislav Smid.