When the Leafs hired Berube, the point was made about a new voice to help push the Leafs further into the playoffs. Berube is the opposite of now New Jersey Devils head coach Sheldon Keefe. Unlike Keefe, Berube is a hard-nosed coach that relies more on outworking the opponent more than "X's and O's" and analytics. Unfortunately, as we saw during the Mike Babcock years and years under Keefe, it doesn't matter who the coach is because the Leafs are so top-heavy on their roster that they can't spread the money out, leading to continuous rollover year after year across their lineup.
According to Craig Button, Berube will experience the same short falls as his predecessors unless GM Brad Treliving provides him with a significant change in the form of a trade of a Core 4 member, which would allow them to spread some money around to balance to the roster.
That balance will likely come with a Mitch Marner trade this off-season or next season when he and John Tavares' contracts come off the books and provide the Leafs with $22M in cap space. As Button mentioned, until that happens, the Leafs will likely continue to be stagnant in the playoffs because they simply have just too much money tied up in four forwards.
