I won't pretend to know everything about DeBoer as a coach but I feel like both his last two firings have been a little undeserved.
6 series wins with San Jose in 4 years, all with a mostly aging core and goaltending that was just average at best. In his final full season there they finished with 101 points despite Martin Jones' career finally nosediving and having a 0.896 Sv% in 62 games (with Aaron Dell backing him up with a .886 Sv%). They somehow made it all the way to the West finals that year with Jones having a .898 Sv% in the playoffs. If that's not getting the most out of a team I don't know what is.
Then in Vegas he brings them to the Finals in his first year as a mid-season replacement, ties the Presidents Trophy winner in points in his 2nd season, then misses the playoffs in his 3rd year. And maybe there's an argument to be made that he could have done more late in the season to push Vegas in but that was also a disastrous season for Vegas in terms of injuries. Their 1C, 1LW, 1RW, and 3D all played less than half the season. They also had a lot of other injuries, including to their starting goalie. There's probably a lot of coaches who wouldn't have been able to muster a 52.6% CF and 52.6% xGF out of Vegas this past season considering the line-ups he had to ice most of the time.
6 series wins with San Jose in 4 years, all with a mostly aging core and goaltending that was just average at best. In his final full season there they finished with 101 points despite Martin Jones' career finally nosediving and having a 0.896 Sv% in 62 games (with Aaron Dell backing him up with a .886 Sv%). They somehow made it all the way to the West finals that year with Jones having a .898 Sv% in the playoffs. If that's not getting the most out of a team I don't know what is.
Then in Vegas he brings them to the Finals in his first year as a mid-season replacement, ties the Presidents Trophy winner in points in his 2nd season, then misses the playoffs in his 3rd year. And maybe there's an argument to be made that he could have done more late in the season to push Vegas in but that was also a disastrous season for Vegas in terms of injuries. Their 1C, 1LW, 1RW, and 3D all played less than half the season. They also had a lot of other injuries, including to their starting goalie. There's probably a lot of coaches who wouldn't have been able to muster a 52.6% CF and 52.6% xGF out of Vegas this past season considering the line-ups he had to ice most of the time.