(I am omitting the considerations of etymology and usage that you raise, which belong elsewhere in the StackExchange network altogether.)
Starting in The Genealogy of Morals, Nietzsche would claim that humaneness needs to be motivated by something other than the wish to promote the good of the group. He notes that we felt differently about 'humaneness' before Christianity and other traditions emphasizing rejection of the material world took over as the majority religions.
In later books like The Gay Science, he explicitly attacks preservation of the species or the nation as goals that are worthy in themselves. He points out that they create destructive emotions in those who relate more naturally to power, among them people who might do great things for themselves, which would then pass on to the society. So the whole notion is not just unstable, it is self-defeating on purpose.
He proposes there is a proper balance between 'master' and 'slave' moralities, noting that our notion of human refinement and proper interactions with other people in Classical civilizations and in other parts of the world that were quite civilized (e.g. Edo Japan) involved honor above compassion and may have actually done more to advance our ability to create better humans.
The global notion of 'humaneness' in general should clearly not be hemmed in by our current biases, shaped by our latest choice of religions and our current level of population and luxury.
There are people who would not care to be treated in what we now label as a humane way. It would not be genuinely compassionate to do what we see as the compassionate thing and spare the life of someone who might hold themselves less honorable afterwards.
This limits our ability to speak reasonably to certain other cultures. And it may ultimately just not be good for us.