I'm going to nitpick this part.
2018 - the "major pieces" they lost were Ian Cole, Jack Johnson, Mark Letestu, Matt Calvert and Thomas Vanek.
* Cole was a trade deadline acquisition that cost a 3rd and a pick.
* Johnson was at best a 2nd-line pairing and a noted defensive wart.
* Calvert was a 3rd liner who'd go to Colorado, play 2 seasons and change, then be out of the league.
* Vanek was a trade deadline acquisition that cost 34-year old Jussi Jokinen and the serviceable, yet quite replaceable (and forgettable) Tyler Motte.
2019 - Bobrovsky, Panarin, Duchene, Dzingel. OK, they lost a shitload here, especially considering what was spent to get Duchene and Dzingel That's been well-documented, along with JK's attempts to keep Panarin.
2020 - they lost no one of any real note. There was a buyout of Wennberg, the trade of Ryan Murray to New Jersey, and trading Josh Anderson for Max Domi and a pick.
So one year where they really lost key pieces, which was the "go all in for the playoffs" drive and resulted in an unfathomable sweep of a 128-point Lightning team. Even if I go back to 2017, it's nothing more than Sam Gagner and post-Columbus he's got 55-72-127 in 342 games, which woefully underperforms his 18-32-50 in that last season in Columbus.