The issue here isn't whether Amazon deserves a cut, it's whether their incentives are aligned with the developers who use their platform. Amazon's control over pricing allows it to make decisions beneficial to the platform as a whole but potentially harmful to the individual developer.
Incentives are never going to be perfectly aligned, but letting the developer control pricing would make them a lot more aligned than they are now.
The issue here isn't whether Amazon deserves a cut, it's whether their incentives are aligned with the developers who use their platform. Amazon's control over pricing allows it to make decisions beneficial to the platform as a whole but potentially harmful to the individual developer.
Incentives are never going to be perfectly aligned, but letting the developer control pricing would make them a lot more aligned than they are now.