I believe you’re on the right track with “creating it yourself” suggestion because you would be able to change what it’s doing. If Apple provided the source code they used to make the OS then the users would be able to learn what it does and change it (if not as an individual then at least via collaboration or a 3rd party). Then the power save would just be a bad, unexposed setting instead of a power-play to get you to buy a new phone.