You made some things up actually and now appear to be speaking on behalf of other members. None of it will resolve the issue so unsure why you are doing it. I will repeat a prev summary of issues noted here:
1- Battery drain, no sudden shutdown, good battery life (90+)
2- Battery drain, sudden shutdown, good battery life (90+)
3- Battery drain, no sudden shutdown, declining battery life (60-90)
4- Battery drain, sudden shutdowns, poor battery life (anything below 60)
5- No battery drain, sudden shutdown, good battery life
6- No battery drain, sudden shutdown, declining or poor battery life
Am unaware which one fits your phone exactly, but am sure one does. They are not opinions, just observations. Even if I claimed The Sky is Pink, that would not pass the opinion test. If you agree with one of the above, your troubleshooting steps differ with each one, and each Apple Advisor will run through every possible troubleshooting step required to resolve it, all the way to hardware replacement. It is a fact. And it you consider any missing, please create a 7th observation.
Some users also have no time to really wait- work, on the go, they need their phones. Troubleshooting, resolving the issue and eliminating the iOS as possibility is a real step. For those next to an Apple store it is a 2 hr effort far more practical versus the next 9 months of future iOS 10 iterations. Or years since the iOS 8 battery forums... So if time was valuable, no idea if some patch would fix it, but a 2 hours step would eliminate a major option in a 100% risk-free solution, I'd jump on it.
Other users have a complicated scenario (like 100 employees with IPhone issues) or no store nearby. I have no advice other than to suggest calling Apple.