Honestly, the .839 says it all. Teams will make mistakes and give up chances. This is the NHL and you're still playing against NHL calibre players. The Leafs have shifted to a possession based game under Keefe and occasionally, you'll give up a rush trying to maintain it. And even with the improved D, you'll still get the occasional lapse. The team itself feels and plays better on a night to night basis, and most of the shot and chance metrics agree.
The problem is, none of that is mattering considering every little mistake is ending up in our own net. This team literally needs to do the impossible and play completely mistake free hockey cause we can't trust our goalies to make a damn save. This can have huge impact on how the team in front them plays too, as they start to second guess things and play a lot more conservatively (which can explain why we seemed to have a lot more trouble generating chances after Rittich went full Lalime).
Any team, even Tampa/Vegas/Colorado, would crumble if they got .839's from their goalies.