If you're in bottom 5 in most goals against I have a hard time seeing sustain success, when you can't keep the puck out of your own net.. Even if you have a top 5 offense and your goal is to win games 5-4 and outscore your mistakes, relying on pure offensive talent.
To me a strong offense but weak defense offset each other and averaging out makes you an average team and wildly inconsistent. IMO
Leafs are essentially built for a Cinderella season, where everything would have to go your way and your offense is on fire at the right time and your lack of defensive doesn't take you out. Your offense can lead you to a Cup and your defense can result in non playoff season where both outcomes are plausible.
Leafs results actually match their team building personnel and Keefe system where you beat Carolina 8-6 and then lose to Florida 8-4 and rebound to beat NJ 7-4 followed by a 6-2 loss again to the Hawks.
You would expect these wild pendulum swings where every game you're not sure if its the opposition net or your own net that will be filled with pucks.