Originally Posted by
Leviatharan
I'm sorry, did anyone expect the order hall campaign to be as cut-and-dry as the quest text being fed to us would have us believe? That there would be no twists?
"Do X." "X is done." "Do Y." "Y is done." "Do Z." "Z... is a bit more complicated." Kind of the mission statement of Legion!
The instant we had the "Tirion" part spoiled, I called that he wouldn't be one of the Horseman, and I'm sure I wasn't the only one either.
Let's be honest here: The appeal of having Tirion as a fourth Horseman was similar to Zeliek, seeing him be a bearer of the Light even in his darkest time. Unfortunately, Tirion... before Ashbringer, he was never a very good Paladin, and the player getting Ashbringer is a pretty permanent way to give that up. He completely gave up on the Light after his son's death, and spoilers for Tirion's death in the first place, Gul'dan easily breaks what little power with the Light he still has - in no small part because he used his one final blessing to finish off Arthas.
He completed his arc, he passed on the blade. To keep him around any longer would've been kicking a dead horse.
Best case scenario, we'd be seeing a guy with Tirion's name and face, without any of his most notable powers or weaponry, to whom agreement to become a Horseman would completely conflict with his established zealotry against dark magic (see: ToGC; we don't need two human Horsemen with the same motivation, especially if the contrast is supposed to establish a penance for one and the second-coming of another), and whose position of authority (as the most powerful knight of the most powerful knights of the Ebon Blade) would trump Darion's again.
I prefer that we got Darion; he's the leader of all DKs on Azeroth but he's been out of focus since he formed the Ebon Blade (after Arthas, your first thought about a DK is probably Thassarian). Who cares if he pointlessly died again to become a super-DK, frankly I found it a little surprising that we didn't turn more of the established DK heroes into Horsemen.