When I backport patches into RHEL, the general process I follow is:
1. For context conflicts, just adjust the patch to resolve them.
2. For real dependencies, backport the dependencies, if possible.
3. If backporting the dependencies is not possible, think of a
downstream-only solution. This should be rare.
People make different backporting decisions (just like structuring
patch series). It can be a matter of taste.
We've done almost exactly the same thing in FreeBSD for the past almost 30 years (with varying degrees of success and nuance, to be true, often limited by early tools). It's an excellent ideal to shoot for, and we've had troubles more often than not the further one gets aways from it.
Warner