While I’m hoping they don’t change him in WCIII, I think the way Daelin is being handled in BfA isn’t necessarily the wrong way, considering where we are.
Remember, we’re in Kul’Tiras now, his homeland. He was beloved and revered by his people, he was their hero. He defended them through the Second War from the Horde. He boldly led his troops to Theramore to rescue is daughter from what the nation of Kul’Tiras perceived to be that same Horde, and was murdered in a great betrayal. He’s supposed to be a hero to the Alliance, or to the Kul’Tirans at the very least.
Compare him to Grom Hellscream. Revered as great a leader, warrior and hero to his people. Not so much in the opposite factions eyes. To the Alliance, Grom is just another blood thirsting Orc doing Orc things. Most could care less that he died fighting Mannoroth and were just happy he was finally dead. That doesn’t discredit the good he did for the Horde (and Azeroth) in his final moments.
I don’t know. For me it seems like this new “light” on Daelin is supposed to be more for the Alliance, and specifically Jaina as she begins to question herself and her choices. The cut-scene where Katherine witnesses the event opens her eyes to the fact that Daelin was on a murderous rampage that couldn’t be stopped, and she basically tells Jaina “No, you were right and he was wrong.”