There's a lot of missed context in that argument, I would say - hinging both on what one labels a "tragedy" and how one defines "building." Referring to the deaths of NPCs, for example, Varian's death led to a lot of new movements within the Alliance, including Anduin's ascension to High King and a strengthening of the bonds between the Alliance leaders heading into BfA and Shadowlands. The major issue for this new revelation in Dragonflight, at least in my opinion, is that the tragedy (the loss of Malfurion to Ardenweald) doesn't really build anything for the Night Elves who are offering the sacrifice, but rather for the Green Dragonflight who gets their Aspect back in the form of Ysera. While I would consider that "building" from a narrative standpoint, or at least rebuilding, it's a net loss for the Kaldorei, who've already lost more than their share, IMO.