I'm really happy for those of you experiencing get battery life with your iPhone 7's. I'm not suggesting this is a problem with the iPhone 7 as a whole, I think it is a problem with my particular handset.
@Hanzu Lao and those of you suggesting it is a problem with my backup - I have been backing up and restoring my phones since my 3GS and I've never had this problem. 3GS > 4S > 5S > 6 all went smoothly, but 6 > 7 had problems. And as I said before, I erased my 6 and restored it back to the same backup and it has been performing perfectly - so I do not understand how my backup could be the problem. To me that indicates either a hardware problem with my particular handset, or some kind of software issue which is presumably affecting a small number of handsets including mine. I'm interested in hearing anybody's thoughts on why the backup could be the issue in light of this, other than personal anecdotes.
@KillaMac - I have attached the last screenshot I took. From 100% to 20% after 4.5hrs of usage (standby isn't in the screen but was around 6 hours). Right now my iPhone 6 is on 30% battery with nearly 8 hours of usage and 10hrs standby. It's not even close.
@T5BRICK - please explain how not charging my battery when it's at 50% is being stubborn?
I didn't mention it in my OP but there were a few other little problems with my 7 that I was also noticing - mostly that some apps like Podcasts and Instragram just stopped showing notifications, and once or twice the touch screen stopped responding for a few moments. Whether it was hardware or software or maybe a bit of both, I'm back on my iPhone 6 now and everything is running smoothly again - the 7 has been returned.
Thanks everyone for your input.
The biggest misconception I see in this thread is that setting up as a new iPhone will cause you to lose your data. It won't. As long as you first back up the phone to iCloud and/or your computer, you'all be able to sync that info after you set the iPhone up as new.
As far as a reason for this, there are myriad possibilities but software that's configured to work perfectly on one device might not always work well when copied to another device and trying to keep all the settings consistent (user settings and system level settings).
Apple acknowledges this and provides a support article on it which advises to backup, setup as new, confirm the problem is solved, and then sync your data back to the new phone from your computer or iCloud:
https://support.apple.com/en-us/HT204686