I have iPhone 7+, actually 2 of them, plus 4 6+, and a couple 6s. None have any problems with battery and iOS 11. They work fine. There was lag with initial updates, then it is simply smart usage--kill apps that you are not using, turn screen down a bit, etc. All is fine. I've talked to others and everyone is overall surprised to here that some people are having battery issues.
Wait on update? NO WAY. We did ours when they came out, still exploring new features. Some I like, others are 'why change things', but that is typical of every major release of Apple or Microsoft products.