The problem here is that you are conflating resolution with how big things are. They aren't the same. I want the resolution on my Macbook to always be 2880x180

The problem here is that you are conflating resolution with how big things are. They aren't the same. I want the resolution on my Macbook to always be 2880x1800. But I want to be able to make things bigger or smaller, while still rendering at that resolution so things don't have to be resampled. (and in the case of the iPhone 6+, the default/only setting requires this resampling). The problem is that when I set it to 'looks like 1680', rather than just rendering things natively at 2880x1800 but a little bit smaller, we have to get into all these scaling hacks (rendering at 3360 x 2100 and then scaling down to 2880x1800), which means you lose the accurate font rendering and clarity you got, everything has a slight blur to it because it's been scaled down.