This is not surprising to me. When I had the S7 Edge, I used to get at least 2 hours more game play time vs what I get on the 7 Plus now. It's always been the Stand-By life that iPhone is still the king of, but there has been several Android flagship phones from multiple manufacturers that have a noticeable longer onscreen life.
Actually with Doze in Android standby time is getting pretty good these days.