As I see it, it's pretty obvious that:
A: This year's Rangers roster is lacking in "toughness"
B: That it is a situation that at the very least, has the POTENTIAL to cause problems for the team in the future.
Derek Dorsett will not last an entire season fighting a majority of guys who are at least 4" taller than him and at least 20lbs heavier.
Brian Boyle, could possibly be the worst fighter in the entire NHL.
Our hardest hitting defenseman is Anton Stralman.
Justin Falk, the "muscle" of this lineup, just got his butt handed to him after facing a real HW
The problem is, the lack of toughness is so widespread throughout the lineup, to really change it, you're going to have to make roster changes that don't really seem available to the Rangers at this moment. As others have said and I fully agree, this team needs to improve its offensive punch more than anything, hopefully by trading for a top 6 SCORING forward.
Because slotting in a "thug" on the 4th line or bottom pair to play 5 mins a night isn't really going to do a whole lot more than adding John Scott did two seasons ago. To be an effectively "tough" team, the toughness needs to be spread throughout the lineup. We will still be icing a top 9 that includes, Zuccs, Hags, Richards, Brass, and Cally. As gritty as some of them do play, it can't change the fact that that's a majority of our top 9 who are below-average NHL size. This is why for me, the perfect addition to this team would be a 2nd line scoring forward with size who isn't afraid to drop the gloves (yes I recognize the extreme difficulty of finding this player). But ideally it would be something like a ryanmalone-downie-iginla-lucic-getzlaf type. Basically what people are telling themselves Kassian will be, while not really acknowledging that over the last two seasons, his development has clearly stagnated, and there's an increasingly probable chance he'll never be more than a 3rd liner.
On defense, I think it's even harder to slot in that "toughness." With AV repeatedly mentioning his desire for more offense from the back end, and the team's clear grooming of McIlrath for the tough guy role, I just don't see who they're going to trade or swap out to be that meanie until McIlrath is ready. As great as it is having three arguable #1/2 Dmen in Staal, McDonagh and Girardi, I'd argue that they're all very similar type of defenseman. As long as those are our top 3 D, you're going to have to try and fill out your defensive pairings with some more offensive-oriented guys, a la Stralman, Moore, DZ. Without blowing up this D, and with Falk under contract as a #7, I have a hard time seeing how the Rangers will find the ice time for a big mean defenseman.
TL;DR Yes, the Rangers lack of toughness is a problem. But it's a problem with a more complicated solution than adding a goon to the 4th line or bottom pair. Unfortunately, finding more consistent offense seems to be a bigger problem at this moment. Therefore without drastic changes that I have a hard time seeing Sather execute in his new coach's first season with the roster, the toughness problem is one that I fear will be futilely addressed at best this season.