I'd rather stick to Smogon's set for Dragon Arceus (STAB/Fire Blast/Recover/CM with 248 HP, 176 Speed, rest in SpA). Being Xerneas bait blows because you can't break it at +1 and it Geomancys in your face and getting walled by any Steel is bad.
Maybe Smogon's set is better. However, if there is one good thing about my set, it's that it might be able to damage Xerneas on a predicted switch in. (Flash Cannon and Sludge Bomb aren't exactly packing Draco Meteor-level power.) You know, nail it before it can even boost. And if that doesn't OHKO Xerneas (without a critical hit that's...don't count on it), it's going to have to choose between using Moonlight right after Geomancy or go on a sweep while hurt. How many Pokemon want to be in that position?
And as for "being Xerneas bait," aren't most Dragons not named Dialga already that?