I think a reasonable middle ground starts with acknowledging that being seriously ill is just a shitty situation, that over a long enough time frame death is inevitable, and that outcomes are often determined mostly by dumb luck. Not being in control can be very distressing, but the struggle to try and retain control often just compounds that distress. Willing someone to "fight" a cellular process within their body probably isn't going to help them in any meaningful way, but there are lots of things that can be done to make them more comfortable. Hope is valuable, but false hope is a kind of cruelty; we all need to be better at accepting the limits of medicine and recognising the threshold of futility.
I don't think believing in metaphysical beings provides any protection against depression. Espcially if you're facing problems you can't solve (i.e. helpless), and your chosen being doesn't come up with the goods. And "in the middle of cancer treatment" would be a bad time to lose your religion.
It seems like the two possible frameworks are fighting vs enduring? (Others?)
If I had to guess, we might choose to position the patient as a fighter because to fight against harsh odds requires courage, so what we're giving is the compliment that you are courageous. I think that's the intent at least.