I'm not saying they're good; I'm just reiterating that I don't believe the issue is strategy (maybe some situational tactics).
The overall strategy of trying to control both slots, push play north, forecheck to force turnovers, and simply get pucks to the net with traffic is sound. There are some tactics that need polish and refinement (e.g. DZ forcing the centre to chase every corner battle so the D can stack the crease was not working) and they're certainly short on horses in some foundational areas (breakout facilitation, down Tanev and to a lesser degree Carlo).
The issue is passivity in the skater group. I get that the regular season is a marathon comprised of mini marathons (games) that are composed of dead sprints (shifts), so some pacing is required. Loved the way Hyman went full tilt every shift, but he was dead by Round 1 when he was with the Leafs, so that's probably not the best approach. On the outside, it looks like they've quit on the coaches. Coaching message to the media is focusing on the positives (where there aren't that many).
Keefe/Dubas system was great for the regular season because the skaters were encouraged to just hold the puck in uncontested ice and rely on super skilled passing and elite finish to make it count. It bore out over many seasons that trying to carry that method into the madness of playoff hockey is meaningless.
I thought this game was pretty stale from the Leaf side for most of the game; they had a couple of good pushes that hit the post (Joshua) or got stuffed (Knies, Robertson), but that's why teams are supposed to try to attack more frequently (shot share stats). They did not breakout the puck well, so they could not forecheck effectively, and generally just played on their flats and heels for most of the game. They were fortunate Chicago is not good and only made them pay a little bit.
A good faceoff play and Knies/Nylander dragging their checks to the slot opened up a goal for OEL and that went straight to everyone's legs. You could see them winning puck battles all over the ice again because they were on their toes and making the Hawks make mistakes. They generated offense per the strategy outlined above: Puck on net through traffic, Nylander heavy forecheck forced turnover, Stecher and Joshua combine for essentially a forced turnover by Knight.