I share some of the same frustrations with you and have the similar fears, but I don't really see Sandin's departure the same way.
Sandin wasn't traded for all in. He was traded to backfill future assets in an all in, so I see it as Dubas still having some consideration for the long term health of the team when we might need the 2023 first rounder to be a player.
Sandin wasn't a player right now. On one hand, you could say he can come back and burn the team by having a long career elsewhere, but even if he's a Stralman or Steen somewhere else, he wasn't displacing anyone in head to head competition in Toronto. I also don't like the player type and skillset, so it doesn't feel like when we gave up on a 21 year old 6'3" do everything defenseman like Kenny Jonsson. He's small, skilled, slow, smart and poor defensively. It's not a slam dunk puzzle piece.