We're not necessarily arguing against screen size, but pixel density. That is, instead of scaling the resolution linearly with the screen size, they did that and some. So now instead of a low 400s pixel density range like the Nexus 5, the Nexus 6 sits at a de facto PPI of roughly 500.

Obviously there's a cost to this, both in battery and hardware requirements to push those extra pixels. Meanwhile nobody can detect pixels on a Nexus 5, but apparently it wasn't good enough.

And next year we'll see PPI at 500-600. I just don't get it.

As for thickness, I think the Nexus does quite well. It's about 50% thicker than the iPhone 6 which is a great number (~10mm) to be at in my opinion.