I can not confirm. I don't know what device you are basing your observations on, but I have been using Win10 on my Lumia930 since 10568 came out for insiders. It was rough at the start because the phone was setting up the OS and settling in. Currently I must say, the battery holds up just as long as when it had 8.1.
10 has many many improvements which I like. Email is a lot better, the Maps app is really nice, Groove a big improvement over XBOX Music and the management of photos with the photos app (in conjunctions with my OneDrive) is also significantly better (as my Surface also runs Win10, everything is nice in sync). Bing lock screen now finally changes the picture every morning, in 8.1 this did not work reliably. Oh, and I have the subjective impression that the Microsoft Camera app is also making crispier pictures.
Although this is still an "Insider" release, I already like it over 8.1. It has enough improvements for me to stay with Win10. At this this build I can not necessarily say that it is "not ready" - definitely it is when compared to iOS 9.0 which came out and was a real disaster.