I don't really have an opinion one way or another with the records, but I will say that Garchomp can win a LOT of battles against Pokemon it often loses to through luck. The Battle Hall Slowbro is OHKO'd by a +2 Outrage (if the Slowbro is level 96), so as long as Slowbro doesn't freeze with Ice Beam, it should lose. He did claim he won a lot of matches by luck, and as long as Weavile didn't appear, Garchomp can beat pretty much anything with a little luck (particularly, avoiding freezes and not hitting itself in confusion).
Peterko, I used the a similar Latias in the Frontier (without Trick support, since I was in the Arcade and such) with the same moves, and I was incredibly underwhelmed by its physical bulk, and even its special bulk at times (it really doesn't like crits). Combine that with the fact that it's weak to Shadow Claw and Night Slash (both of which have high crit rates), and the fact that Gallade is weak to Shadow Claw, and I'm frankly a little surprised it did as well as it did. Have you thought about DD/Sub/Waterfall/Outrage Kingdra in the second spot? It doesn't have the awesome Ground immunity that Latias does, but Registeel resists its only weakness, Water/Dragon STABs have insane coverage. That would take care of Flare Blitz pretty well too; I'd think your biggest problems would be getting hit by fast status before Kingdra got a Sub up. I haven't tried it in the Frontier yet, though, so it may be better in theory than it is in practice.