The Leafs are proud of their data-driven approach. So here's some data to help understand where the problem is:
In the past 4 playoff series Toronto is 7-5 in the first 3 games of those series, 3-8 in the last 3 games (2 games for the Columbus series), including 1-5 over the past 2 series. In series-deciding games they've scored a total of 3 games in those 4 years.
As series progress typically there are less powerplays, the scoring comes down as the games become tighter checking. The very simple conclusion then is that this team cannot win tight-checking, low scoring games in the playoffs. And they're not "getting close", in fact the 1-5 stat shows if anything they are getting worse at it.
So the challenge for Dubas and Keefe is to sort out how do they get this roster (as is, or with changes) to be able to score when their opponent is making it more difficult to score. Clearly, their stars so far have been unable to.
Matthews, Marner, Tavares and Nylander specifically seem to be able to put up solid numbers overall (as do most teams' best players), but in those critical late-series games they, or anyone else for that matter can't buy a goal. That has to change. And again, it's clear they are no closer to figuring that out than they were 4 years ago.