Not only that, but a little less acceleration, and a little less power and accuracy on his passing and shooting, and Karlsson goes from being a fragile but offensively dynamic player to being a liability who doesn't generate enough offense to even approach his cap hit. Remember two seasons ago - outside of a five-week period of legitimate excellence, Karlsson was just awful, and that's without really being hurt much.
Burns is honestly in the same boat - at his age, he should be slowing down every year, losing a little more power and accuracy on his shot and his passing, tiring out a little more quickly, and those things can add up quickly. He's not exactly a defensive wizard and has to rely on his offensive generation, and I honestly think that's somewhat in question already - he picks up points, but I don't think he's really tilting the ice as much as those points indicate, and he's giving a lot back on his weak blue line performance (odd man rushes, puck fumbles, plus his notorious lazy icings).
Couture could see the same declines, and Bonino. Vlasic is bad now and could go right to unplayable on a bad team quality very soon (he's already not far from it, if not actually there). Reimer could regress to backup quality. All of this is without considering the possibility of injuries.
This team, as constructed right now, could easily be Montreal-bad; all it'll take is some injuries, some age-related decline, and some young guys either not developing as quickly as we hope or turning out to be flashes in the pan. Some of all of that absolutely is going to happen.