I think it's more the fact that software hasn't kept up with hardware advances. Even the iPhone 6S with it's amazing SOC does the same things every other new phone can do, albeit fractions of a second faster. After an initial "cool", you go back to doing the same things you did last year.
I do think cameras made a big jump in daily usability and quality from 2014 to 2015 and if that jump can continue in 2016 (e.g. Samsung's rumored 12MP camera with f/1.7 lens and a big sensor), that alone would be worth a purchase for me since my phone takes 98% of my baby's pictures and videos.
Besides the camera, I do think everything else has plateaued in regards to daily usability - whether it be displays, SOC, biometrics, and so on. Yes they're faster and better but they don't materially improve your experience.
I don't think we're going to see a real advance until one of the following there's a significant step forward in usability. For example - foldable or expandable displays that don't compromise mobility, size, or weight - go from a one handed 4.5" phone to a much larger two handed phone display.
I will say that I certainly hope that someone steps up and moves the market with 32/128GB storage options for $100 considering how cheap storage is.