When your leadership core, the "letter wearers," consists of McD, Girardi and especially those towers of evil, Staal and Stepan, no 1 or 2 new players are going to make a difference. Especially if they are 3rd or 4th liners getting 10-13 minutes a night.
Caps aren't tough because Wilson runs around on the 4th line. Caps are tough because Ovi plays that kind of game and they have guys who hit to hurt and like messing with other team's players on almost every line. A guy like Wilson simply fits in and follows that team's leaders.
Same with Pens. Crosby drops the gloves when he thinks a teammate might've been wronged. Malkin is meaner, granted, usually in a really cheap way, than anybody on NYR. Towes is like Crosby. He doesn't think twice about jumping in for a teammate. Keith is meaner than the entire NYR team put together. Simmonds, Voracek in Philly.
It's all about the leaders and best players who log heavy ice-time. Dressing a 4th liner like Glass or even someone much better who still doesn't see the ice when most of this stuff happens is really ineffective. Especially with the instigator rule and the way today's game is officiated.
Even when we trade for a guy like Nash, someone with size and actual fighting ability, NYR end up with a guy disinterested in physical contact the vast majority of time unless confronted and repeatedly provoked. There's something about this franchise.
Our chosen leaders? McD, Girardi would have to be forced into it. Simple hitting and consistent physical play doesn't come natural to them. And Staal and Stepan? That's like a signal for the end of the world if Stepan is involved in a real altercation.