It will always be the driver. The question is always going to be whether we spend X amount of resources to get Y probability of restoring Z health to someone (or someone to Z level of health.)

Costs are just another way to say resources. If we only have $100, and it takes $100 to have a 33% chance to give Bob a 50% better life, but $50 to have a 15% chance to give either Sara or Rose a 100% better life, we need a rubric to make that decision.

We can't just do first come first serve (maybe the first person in line takes all the health care for a 1% chance of getting 1% better), or pick the person we like better (who is we?). We have to figure out how to manage and grow the limited resources we have. We manage them by coming up with algorithms on how to spend money, and we grow them by cutting costs and investing. This is better when it is done in public through democratic means than when it is done behind closed doors (to avoid the above problems.)

There will always be death panels. There are currently death panels. The reason for single-payer is not to avoid trying (imperfectly) to maximize these equations, it's to get rid of massive amounts of administration and graft (cutting costs.) If all that savings goes to the Pentagon, we wouldn't be any happier than before single-payer.

But it's not good to come up with some fuzzy way to determine who gets treated. Efficient spending is a way of minimizing injustice. To say a health system is not being driven by costs is just another way of saying that it's going to be driven by undeclared and unexamined biases.