it's wrong though.
This image is posted every time and it proves more PPI is a good thing, and not wasted. There are more things to display other than images and english text.
I wonder what the top image looks like when you blow it up 8x its actual size...
Your point is dumb.
There is a natural limit to your visual acuity. It's a little more nuanced than the conception of 'retina' that's been bandied about, but that concept is nonetheless a good rule of thumb to let people know that anything beyond that point is on the steep side of diminishing returns in terms of its efficacy.
600ppi might be useful for esoteric vernier acuity tests, or the double line/single line acuity test (i.e. is this line 2 lines, or 1 line?) but by and large, that's just not a factor in 99% of the images and text we view.
That said, these continued increases in smart phone/phablet sized screens is excellent news for me; these (or similar) panels are used in VR headsets, in which I have the highest degree of interest...