If we look at it in pure physics:

Power is the rate at which your engine can convert energy. In this case from chemical potential to kinetic (and heat etc...).

Whereas torque is the twisting force your engine can produce. An hence the most efficient.

So if the powerband is defined as a point where your bike 'kicks you in the arse and wants to destroy the horizon' (in technical speak ofcourse) then you would have to say it is the point in rpm where the engine got a whole lot better at converting chemical potential to kinetic energy (assuming small changes in amount of chemical potential relative to power change) and hence your peak power.

But if the powerband is defined as the rpm range where the engine is most efficient then it will be peak torque.

I submit the powerband is the former From experience...

To the best of my knowledge this is right. But some people do have a habit of ripping into newbe bikers