I haven't had the same experience. I have a 950 and that got about the same battery life as my 6s. I'm probably not a heavy user, I always end up with at least 30% at bed time. Like others have said I miss the live tiles and the UI. Widgets are not substitute for live tiles no matter how much we might try to make ourselves believe that they are.
For me the app "issue" isn't really a concern. I switched to iOS (for a few weeks) and back to W10 earlier this year, and didn't really miss any apps. Sure I have more on my iphone, but I don't NEED them. The ones that I use on a daily basis are available on both iOS and W10.
I do still use most of the Microsoft services (Outlook, Onedrive, Groove, etc.), though they do seem to have just changed something in the last week or so and my shared calendar with my wife doesn't work.
I will try to embrace more of the Apple ecosystem of services to truly get the most out of my iPhone this time. Like I said I'm committed to using it for at least a year (just something I did for myself, not a contract or anything like that). I am still keeping a close eye on W10 though.