> According to Kilburn, HTC’s consumer research shows people prefer thin smartphones — between 8 mm and 10 mm thick — as opposed to thicker devices with longer battery life.

One data point, but that's what HTC's claiming their customer research shows, and Apple's trends suggest their internal data points the same way.

There's clearly more than the one option going into the choice here.

That's not particularly thin, both Vivo and Oppo have models under 5mm. The former even managed to keep the 3.5 jack in the 4.75mm X5.

I think it'd be interesting to have an experiment where some flagship phone (like the Galaxy S*) is sold in two versions, one with double the battery life but a little thicker (and cases for both sizes are available), at the exact same price, to see which one people really prefer. Personally, I'd certainly go for the double-capacity version, but considering how popular iPhones are, I'm under no illusion that my tastes represent the mainstream.