Is that something that applies to most people? What if many find it beneficial or at least fine where it is?It's not that people can't change their habits. Obviously that's easy to do. The issue is, why should they have to?
Apple used to care about ergonomics. They used to make phones that "feel good in the hand". They also used to be the leader in smartphone photography and if I'm not mistaken, the iPhone was the first smartphone to use the volume rocker as the camera shutter.
IMO, the current placement of the power button is not beneficial in any way. They moved it down from the top to make it easier to reach, but it's still too high up to reach one-handed and now, it's an impediment to using the volume rocker.
The answer isn't always to just suck it up and change. If it were, you could justify all kinds of dumb design decisions. The user experience is supposed to get better over time.
I'd bet that there would be similar discussions popping up about people finding it bad if the power button was left on top. Or if the power button was moved lower down. Or if it was somewhere else. So based on those complaints from some, would that then show than any placement is therefor a bad design?