On the whole imessage argument, even if I had an iPhone again, I'd still use WhatsApp more. I rarely use the basic messaging app anymore on any phone, but I'd prefer to be able to have conversations with anyone on any brand of phone. If I need to get in touch with my old grandpa then l lift the phone cause he's not wanting to sit painstakingly typing a message on an iPad when he can just talk.
The one thing that stops me going back to iPhone though is the most basic thing. I want a picture as my background. Not a bunch of random tiles. If I have a great picture of my son or daughter then I want to see it on my phone. Maybe you can do this on the most recent iPhones though? It's been a while since the 4s!
Both systems are great, and both have their flaws, but I'd agree that new phones are coming out now just for the sake of it. Look at YouTube and you'll see antutu scores etc of every phone. Woopdee doo. In reality I'm happy to wait an extra second or two for an app to open and have that extra cash for something else. Currently using an LG g4 which has a qhd screen, runs perfectly, has a very decent camera and I can replace the battery when it dies and add memory via a memory card slot.
I'm happy to pay a premium for something if it does justify the cost, but for the majority of people who buy a new iPhone (or Samsung etc) , it'll just be used in the exact same way as their old phone! But it's shiny and new and has no bezels!