Hiding under the stairs isn't a cheese imo. Maybe a little cheap, if you wanted to call it anything, but not cheese. He can still hit you, you can still get hit by phalanx/legionaires if you stand too close to the boxed, phalanxes love to stand between you and Valus, and it seems that under the stairs was designed to be a cover spot, as there are gaps perfectly placed to where you can see Valus on that side.