Type does not matter you say?
Try Earthquake STABBED from Garchomp hit on Metagross, although Metagross is able to survive one and strike back at Garchomp with an Ice Punch
Starters, Spiritomb VS Skarmory, Skarmory sets up Spikes and Roars away, Spiritomb won't have any real chance against Skarmory, it's only move to be using is Will-o-Wisp
Now, what really causes Steven problem's are Cynthia's Lucario and Garchomp, Garchomp is taken care of by Metagross, Lucario is still a threat
Cynthia's Roserade would be murdered by any of Steven's Pokemon
Cynthia's Milotic is eaten by a Thunderpunch from Metagross, Energy Ball from Cradily
Garchomp and Lucario are the only Pokemon to do any damage on Steven's team
I'm not saying all these by favorites, it's just the truth, I am NOT saying Steven beats Cynthia, after all, anything is possible with these horrible CPU AI =P