I think that Riot wanted to make his ambition more clear, give him a clear goal instead of being "mysterious", which is fine. However, I think they lost some of Aatrox's main thematic with the goal they gave him. Old Aatrox was also a scary force to be reckoned with, but he was somewhat neutral: he fought for the losing side in a war. That could be seen as heroic, or it could be seen as perpetuating the horrors of war. And he was extra scary to the enemy side.
What I like about old Aatrox's theme was that he gave a subtle commentary on war. One old line I vaguely remember from his lore was something like "after their victory, the victors realized what they had truly done" meaning, even the victors of a war have to commit horrible atrocities, because that's how war is. We have many factions in League that glorify war (Noxus and Demacia being the big ones, most of Freljord) but Aatrox served to show that war isn't always heroes and glory. War is scary and menacing like Aatrox himself, even to the winners.
If they wanted to streamline him a bit, give him goals and make him more compelling, I would have made his goal to perpetuate war. This would be for the detriment of Valoran and his gain. A war that is about to end, the losing side is failing, and then Aatrox swoops in and helps them win the battle so the war continues. I think newer Aatrox's attitude and story can still work, but some of his neutrality is retained.
That being said, I am looking forward to the full lore to see how they handle this, but I agree that the somewhat neutral nature of Aatrox's actions was the cool part of his lore.
