Just a thought, and the proof of this theory is not 100% out there, but there is some.....Do the leafs not match up well, in general, vs teams that are very young with a lot of 'high end' draft picks who may or may not have turned into good hockey players yet? Meaning...
Buffalo and Ottawa are NOT good teams this year, but they are 2 of the youngest teams in the league with a lot of high draft picks, and Toronto sure had problems against them, both of those teams often making the Leafs look like the far inferior team.
Columbus is the 2nd youngest team in the league, Leafs had one convincing win, but also a loss versus them, one of the worst teams in the league.
Chicago. Again, a very bad team but with some very young (and with Bedard high end talent) that makes the Leafs look bad, not the other way around.
Montreal is not all that special either, but they are the 3rd youngest team in the league with some raw talent. Both games against Montreal have been very close.
The best games the Leafs have had all year have been versus Minnesota, Dallas, Washington, The Rangers (at least one time), all older and very veteran teams. Even the impressive win against Nashville was against a team in the middle of the pack in terms of age/experience. Even Boston, a pretty veteran team the Leafs take to OT. But the Sabres hang 15 on them in 2 games and Ottawa puts 13 on them in 3 games.
Usually (not all the time, but usually) when they play against an older, 'less athletic/slower' team the Leafs fair well. Put them up against some very young, high end/fast skating talent (even when those teams aren't doing that well) and the leafs have problems handling those teams.
My point is that it may not be the Leafs playing up to (or down to) the competition. It might simply be the teams that they can outskate and outlast physically they do well against, but a team that can go stride for stride with them, maybe even outskate them and match them in skill (even if it is raw and not fully developed), that is where they have issues.
Leafs record vs the 10 youngest teams in the league so far: 3-7 (and the 6 worst teams in the league are in this group) and the leafs have lost by 3 or more goals 5 times this year, 3 of those 5 times vs this group. They have allowed 54 total goals in those games. (5.4 per game)
Leafs record vs the 10 oldest teams in the league so far: 8-3 Allowing 27 total goals in those games (2.45 per game)