I may have read too much into your original post. I think I get what you're saying now.
We apply the concept of intelligence to other species, so I don't see why we couldn't apply it to machines. If people want to redefine intelligence so that humans stay on top, then they are wrong to do so. There is undeniably an objective component to it, even if there are many cultural factors at play as well. If you don't like the word "intelligence", replace it with "competence", "productivity", "performance", etc. and the same argument will apply.
You raised two other issues: the possibility of AGI and the utility of AGI.
I think we have good reasons to believe that it's possible. Three possible future scenarios: (1) we get to the point that we can simulate brains to a high degree of accuracy in software, (2) we get to the point that we can build artificial brains out of neurons made of silicon, (3) we get to the point that synthetic biology is advanced enough that we can engineer new kinds of intelligent organisms. These might be science fiction by today's standards, but they show that there is no issue with conceivability. As an aside, the human brain runs on relatively low power consumption and operations per second, so computational power isn't a bottleneck. We have enough compute, we just don't have the right algorithms yet.
As for the utility of AGI, I strongly disagree that there is no market for it. By definition, an AGI can do anything that a human can do. There is already a job market for humans. As soon as AGI can compete with humans in domains like management, engineering, scientific research, education, etc. I don't see why there won't be a huge economic incentive to adopt it.