The one aspect missing from Despres' physical game is his willingness to step up for a big hit. He's more than capable. Just needs a steady partner and confidence.
He's a beast along the boards now, and more than fine at clearing the net front.
Firstly, that type of play, and making those types of reads will come with time. Stepping up on guys like that is an art form, and very few Dmen can do that consistently without going way out of position a lot of the time. Frankly, I am very happy, as Despres is developing if that isn't a part of his game if he's doing everything else right. Having good gap and a good stick, playing the body instead of playing the puck, being HARD on the wall as he has been, and being tough in the corners and in front of the net, those things are all much more important. He can be intimidating enough that way, and if he's playing with a guy like Bortuzzo who already is looking for those open ice hits, it's better if his partner isn't.
Also, what some people don't realize or remember: Despres' hallmark as a prospect and younger player was never about his physicality. His nature was never that of an Orpik, Stevens, Kronwall or Trouba. Despres was a guy who was just incredibly gifted physically, and has a very intriguing package of size, speed & skills. In junior, he often dominated physically because he was a man amongst boys and just SO much bigger than everyone else. A little bump is all he would need to separate guys from the puck.
But the nastiness you're seeing in Despres' game right now is not something that has been there all along. It's very similar with Bortuzzo when he was younger. This type of toughness and physicality are attributes that these guys are learning and are being cultivated by them and the coaches in WBS and in Pittsburgh. Even when Despres played at the WJCs, he was asked to play a physical & shut-down style, and it was a new type of role for him (which is why he didn't look particularly good or have a strong tournament).
Also, these young guys like Bortuzzo and Despres, who do not have the skills of guys like Letang/Karlsson/etc., or the insane poise of guys like Maatta or Ekman-Larsson, at some point they realize that if they're going to really make it in the NHL as impact players, they're going to have to adjust their game and use their god-given strengths. And it helps when you have a really strong group of prospects who these guys are competing with, helping them realize that they have to play a certain way if they're going to be the ones who make it to that top-6 ahead of the other guys.
So while it may seem like there's a thing or two lacking, I can tell you: the amount of physicality that Despres has added to his game since junior, and the way that he has refined/changes his style of play, is actually very substantial.