To all of you who have worse than expected batteries: Do you ever let your phone get really hot?
For example, sitting in a cradle in your car in the sun doing navigation was you drive can make the phone get quite hot. Same deal if you're at the beach and leave the phone out in the sun. Heat degrades batteries very quickly.
I know of a couple launch day iPhone 6 units that are still at 85% and even 90%. They've been kept out of extreme heat their entire lives. My iPhone 7 Plus is also doing great at 90% after nearly two years; same deal. The only iPhone I've ever had whose battery seemed to weaken early was an iPhone 5, and I had it back when I was going to the beach more and it would cook in the sun. Bad past me, no time travel biscuits for you.