Like I mentioned in my previous comment, I get that at a certain point you want to actually see the individual pixels, and you are correct that using bilinear at that point would not be appropriate. But the zoom levels between 100% and that point (excluding exact increments of 100) look really bad in AP and do not represent what the image actually looks like.
Here's another comparison that should illustrate the problem. The left image is a screenshot from GIMP of a section from the original image, with the canvas zoomed to 125%. The middle is a screenshot of the same section of the original image displayed in AP, again with the canvas zoomed to 125%. For reference, the right image is the same section of the original image, unscaled.
To me at least, it's pretty clear that GIMP is doing a much better job at representing the original image. And when you zoom in close enough with GIMP, you can see the discrete pixels fine without any blurring. This is the behavior that I've seen in every other photo manipulation/painting application that I've used. I'm sure they all have different implementations, some better than others, but none of them distort the image this much. The stair-stepping and varying "pixel" sizes seen in AP here is not representative of the original image, it's an artefact of using the NN algorithm in these scenarios.