I agree with your Tavares point. I think he made a huge mistake prioritizing forwards over defense. I think that's what cost the team the first few years in the playoffs. He has been trying to rectify the situation ever since. The 2021-22 version of the Leafs was the best version yet. Mostly from internal improvement from the drafted defensemen and acquisition of a Giordano. They had the Lightning on the ropes. The series was about as equal as any during the playoffs. They lost. I'm glad they lost. However, there was no shame in losing to that Lightning team.
As far as Dom's model goes, he explains the change right here in his preview:
"To those that would listen, I often preached patience with the Islanders’ rating per this model. Many cited the Trotz effect and without any explicit coaching effects baked in, it would take time for that to settle in. That was especially true for a team whose focus on shot quality over everything wasn’t easily accounted for by public analytics.
But that also ignores that last year was a very different season for the Islanders compared to the first two under Trotz, where a bridge between eye test and analytics was finally formed. Islanders fans screamed as loud as they could that this team controlled quality to an elite degree, but it wasn’t until last season (or the 2020 playoffs rather) where that claim could be backed up by public analytics. In 2018-19, they were a solid 51.1 percent expected goals team, but that dropped to 49.9 percent the following year (with a below average actual goals rate). Then in the playoffs, the team finally turned it on and didn’t look back over the 2021 season. The Islanders had a 53.9 percent expected goals rate driven by elite defense last season, ranking top five in both categories. Before an injury to their captain, they were even higher."
Dom's model is just a derivative off of xGF. It has evolved away from something like CORSI/FENWICK, which just valued quantity over quality. Dom and other public models were very high on the Isles coming into this season because of the above points. The Isles became an elite defensive team with above average goaltending. Last year their defense took a huge hit, despite having improved goaltending from Sorokin. The reasons for that can be debated ad nauseam (COVID, road trip, taxing style over 82 games, Chara and Green in the top 6, too many middle 6 forwards, etc).