Is anyone actually suggesting that Russia would have won the World Cup if only they had a better coach? To me, that is just ridiculous, particularly suggesting that a foreign coach would have some kind of mystic genius that would turn Marchenko, Orlov and Kulikov into shut-down defensemen. Russia cannot win best-on-best tournaments because they lack an adequate defense (and really, offensive players as well, when you get beyond fancy stickhandling and passing as well). Yes, coaching is a big problem for Russia, but the main issue, in my opinion, is a lack of competitive hockey players throughout the system.
Looking at defense alone, I think it is fair to characterize the Russian defense group as slow and small. These are two deadly traits when playing against top-end forwards. Look at how easy it was for Canada to push the Russian defense around, knocking them out of the way and golfing at loose pucks until they finally went in. If they had better skaters on D, maybe they could have done a better job of clearing pucks out of the zone, but that has always been the Achilles' heel of the defense.
However, in the next breath, I would say that Russia didn't play badly. I thought they played up to the level of their capability, given their weaknesses, and showed a lot of fight and passion and commitment! I don't think it was a lack of effort. If they could somehow put together a defense that could support more offensive pressure, you might see a different result!