I remember with iOS 9 they specifically focused on extending battery life. Let's see what 11.3 and later do.
Yup, I recall thinking of both iOS 6 and iOS 9 as "Snow Leopard-style releases" in that they didn't add much in terms of new features but rather focused on polishing performance and battery life.
The thing is, I think, that OS developers (not just Apple and iOS) are too focused on releasing new features and changing the UI instead of optimizing core performance and cleaning up code. Most average users care little about the OS itself and more about how the device performs while running apps and doing tasks. I couldn't care less about the design of the Messages icon and cool new features like "Hey Siri" or raise to wake - what matters to me are things like not having to keep my phone constantly plugged in while playing Spotify in my car. I'm sure many others would agree. Let's see what 11.3 has to offer.