I've actually found Genex to be effective against mill. Tribute Ultimum over and over to summon Genex Army. You get to pop a monster with Genex army, but then afterwards, Ultimum allows you to put at least 2 cards back into your deck with its effect. Genex isn't super great against the other OP archetypes, but it helps. Alternatively, swarm the field decks that don't require milling on deck work.