Ethics aside, making the Space Marines pay-to-play while Orks are free would be hilarious, especially if the Orks still have higher odds of winning. Being a walking tank isn't pay-to-win. You have to coordinate and not get overrun by sentient mushrooms with extra-shooty red guns. Get a few veteran tabletop players to pony up, and they'll slice through a hundred randos without slowing down... while the survivors think it's the coolest thing they've ever seen.