I will start backwards from your post:
- Arms length is a guidance invented when displays were 17". Online monitor positioning guides state "one arm length, but if your monitor is big, move it further". 32" at arms length is no ergonomic, it has to be at least one and a half arms length away. The proper guidance is using angles of viewing that will not cause too much neck/head rotation, but I will not go into that, if you want you can research on the subject (we have a whole department in our company doing just that, and they adjust our workstations each 6 months to make sure no repetitive stress injury).
- PPI and "retina" is relative to the viewing distance.
- It is a fact that ASD has a higher PPI, and the Dell has lower, but it is also a fact that the ASD is 27" and the Dell is 32". I am not sure what is this general misconception on the internet that you have to view the display at the same distance...
- Proper retina can be achieved by PPI and viewing distance together, not by one of this. The article you quote does not account for viewing distance, so is not a real scientific article. It is one thing to view a 21" monitor at arms length, and another to view a 32". One arm length is not going to be proper in terms of viewing angles.
- If we went by "retina" invented term, then our 75" inch TVs should be 16K. But they are not, they are 4K, because we watch the from farm away, and we do not see the pixels.
- I would not want to have the ASD in front of me for a second because of its terrible reflections - I see myself and all surroundings. It feels like a mirror. I had iMac 5K, as I stated above, and I sold it.
- 4K is a high DPI display, and depending on the size, you only have to adjust the viewing distance for it to become retina. Try it for yourself. Read ergonomic guidance in terms of viewing angles and neck/head rotation and tilting, and you will see what I mean. If 32" is too close, you will suffer from too much neck/head rotation/tilt to see the peripheral of the screen.