Take a look at Bernier's stats. He's been in 385 NHL games and has 159 points in that span. If that isn't a proven NHL player, I don't know what is. Show me any 4th line player in the NHL who has those kinds of stats and is 26. Maybe there are 1 or 2 that are not coming to me off the top of my head, but it doesn't matter. The point is that Bernier instantly makes the 4th line much better.
He had a lot of top six time earlier in his career because of his draft position and he still never distinguished himself. Maybe he can reinvent himself at this point, but he wasn't exactly great last year playing for DeBoer in a similar role.