There's absolutely nothing wrong with skipping the current year's iPhone. I don't know why people have this mentality. For any brand, really. Most new phones nowadays are incremental upgrades, not "evolutions" so to speak.

I'm on my iPhone 6 (not even the 6s) right now and I'll be upgrading after three years of having it, but only because the screen is shattered, battery life is bad, and sometimes it's a bit slow.