I might as well make it official, Uxie/Heatran/Garchomp lost after 489 wins. I faced some bad luck and decided to break one of my rules. Toxicroak poisoned Ux turn 1. I think I used Scary Face twice, and continued to stall it out of Poison Jab, so that Ux could Yawn and Memento. Struggle got a crit on the switch, causing Uxie to only be able to Yawn. Garchomp put up a sub and Sword Danced on the next turn. I was supposed to attack. One sub and one SD is usually better than two SDs and no sub. I knew that a Toxicroak crit would kill it and leave me subless. I was irritated and went for it, much to my regret. Anyway, it only gets worse. I took out the next pokemon, and then Infernape shows up. It had a plus speed nature(16%). Down went Garchomp. I was happy to see that Heatran survived a Close Combat and did like 75% with Flamethrower.
Peterko, I'll update my OP with that, so that you don't have to link to this post.
The good news is, this happened a while ago, my new team is currently at 448 wins.