This is your feeling and apparently ONLY YOUR feeling. I only started mentioning our SCF futility this summer when I read a list of teams in the 4 major sports and their time between visits to the final round. In the NHL we are 2nd longest. Only the Maple Leafs are suffering a longer drought.Not winning the cup is being used as a cudgel against anyone who doesn't agree with a full on rebuild. Whether the Islanders lose in the first round, the ECF, or in game 7 of the Stanley Cup Finals that "argument" can be used to justify the position. I think it's incredibly broad and, quite frankly, silly.
I started pushing for a rebuild 2 years ago. Not because of any playoff shortcomings, but because the makeups of our roster isn't balanced right, along with my belief that who would be our most productive players were already hitting the other side of 30 years old and will have contracts that are expiring in their early-mid 30s. Those are not players I would want to resign at that point, and with a weak prospect pool plus no success signing high end UFAs, trading the likes of a Nelson or Barzal back then could have solved so many of our problems. Unfortunately, that path closed to us for good when Lou traded for Horvat.
Everything else you put out in your post is based on your own take on what is acceptable as far as playoff performance. If we don't win X number of rounds, tear it down. I base my call for a rebuild based on roster makeup, the direction of the style of play in the league and our ability to compete against the teams in our own conference. I also based it on our ability to replace players as they age out. In a hard cap league a team needs a good stream of home grown players. We haven't hit on players that can score can't attract them on the open market and only this year do we finally have a 1st round pick.
All the extenuating factors that made us an undesirable destination are gone. The Islanders aren't the side show they used to be. Yet when I look at this team today, just as I did 3 years ago, I don't see a team that is built to compete in this league and doesn't have adequate replacements in the system. In fact the Capitals game just reaffirmed to me that if we make the playoffs it will be because our goaltending dragged us there, not because of we defend well or can roll 4 lines with balanced scoring.