You've got the idea of the move wrong.
Here's the explanation for Wonder Room:
>The user creates a bizarre area in which Pokémon’s Defense and Sp. Def stats are swapped for five turns.
What I think you comprehended was that there is a swap between attack and defense, when in fact attack (or special attack for that matter) have no relation at all with Wonder Room.
Also the opponent's defenses are not lowered in any way, just swapped.
Hope I helped!