I was playing Untap, and I had a Cumber Stone out that gave all opponent's creatures -1/0. He casted Warstorm Surge, and proceeded to drop a bunch of 5/5s with Omnath, Locus of Rage. He said my artifact's effect doesn't kick in until they are already on the battlefield, but since it's a static effect I think they would be 4/5s when they enter. Am I wrong?