Yes, only CM varients of grassceus can beat mono kyogre since support sets almost never have it.
Lead thundurus with twave/taunt/tbolt?/focus blast is actually really good as it can 2hko support dialga and twave the stuff which comes in to revenge it, which are usually scarfed. Never used it myself but I've met it a few times when laddering and it is a huge pain in the ass if using defensive SR dialgas instead of LO.
I only play Ubers. Known alts on PS: Splendiferous, Flying Petals, Shining Smile; peaked #1.