Great post azircon.
Whilst disabling rentals for survival is one way to do it, what do you think of reducing SPS rewards for each rented card in deck (-10% per rented card). Similar to what it is for using starter cards in the other modes. That way it still makes rented cards have some additional use but for those using purely rented cards their rewards will be massively reduced to the point where it wouldn't be profitable to do so.