Man this guy is exhausting
Just like in politics, someone will argue, with some justification, that the current president is living off the momentum, etc. of the last one. Most will say that the President (GM in this case) who is in power at the time of any specific success gets credit. Stars in finals for first time in 20 years, the balance of the moves made by Nill are the reason (and players playing great, of course)
One thing not mentioned is the players Nill elected to let go as part of the rebuild when he came in, guys like Dillon, Eakin, Garbut, Roussel, etc. The same guys complaining now were probably (from memory, but not sure of individual posters) calling all of them "total trash" as well. And, also correct to some degree, but Nill had the vision as to how to supplement the players he inherited, who to hire as coaches, which is a GM skill, too. I doubt any team ever traded every single player drafted or acquired by the previous GM, not if they were good. Again, sum total of moves has proven to be pretty good. Some fans argue for perfect, which just ain't gonna happen, because it never has.
I would put perfect GM'ing at building a contender in 3 years, and then actually contending for 3 years, as that seems to be what it takes for most winners. We thought we had that in 2016, right on schedule, but it went backwards, and he went into the next three year rebuild mode, with a few forced errors (i.e., hiring Hitch, not all his fault) and here we are. Probably a contender last year, lost to champs, definitely a contender in year 4 of phase 2.
Again, not perfect, but not bad either. 30 other GM's would love to be in this place now. And maybe 20+ have never gotten this close to a Cup.