The point is things got worse from iPhone 5 -> 6 .. the case got less resilient. So its a downgrade.
Parent is saying people want durability and better battery life and would gladly sacrifice thickness for it, not sacrifice all the things that iPhones have and those old Nokia's didn't.
I'd happily take the iphone 6, add 20-40% in thickness and weight, make it more durable and have a bigger battery, and let the phone sit flat on a table (as opposed to the camera sticking out like now) without having to mess with a case.
iPhones always outperform Androids in battery life in the real world IME (there are exceptions that probably break the rule, but with compromises elsewhere I'm not willing to make so I haven't bought those devices). My 6+ is living up to the "2 days" claim.
I absolutely wouldn't trade thinness, and more importantly, weight, for longer battery life.
The battery life is fine. The weight is good. The thinness allows me to add a case and still only have it be as thick as an iPhone 5.
For me, someone who actually paid for an off contract 6+, they made the right call.