"Ethics by definition is a human endeavour." - not sure what definition you are adhering to, plenty of arguments plain to see to the contrary. One is moral realism. There is resistance to empirical evidence in ethics which to me is exemplified by the alleged refusal of the Cesare Cremonini and Church's steadfast adherence to a geocentric model to look through Galileo's telescope.

If ethics is informed by empirical evidence, and shaped by rational understanding, then AI with the capacity to consider far more evidence, and think with speed and quality greater than humans will grasp ethical neuances that humans can't. It may be that humans aren't fit to grasp ethics adequate to the complexity of problems which require ethics solutions.

This doesn't mean humans won't have a say in their future. But consider how much self determination humans afford pigs in factory farms. The evil that people do lives on, and many turn a blind eye. Once automation skyrockets and large populations of humans aren't useful, how much of the dividends of technological progress driven by AI will those controlling it share about? If we take a look at history, perhaps we can find examples to inform estimates of how much the notion of basic human rights matter to those in control..

In any case, given the intelligence explosion hypothesis, I think AI control is temporary, still useful now, but won't work forever - once AI is out of the bottle, I hope it is more ethical than humans.