Than you should go see a medical scientist or something. Every optical device including human eyes have a limit of resolution. I don't see any pixels on iPhones after the release of iPhone 5.I have an iPhone 7 Plus, iPhone SE and iPad Pro 9.7" and of the three devices I notice the pixels more on iPad too.
When I criticise the se display I don't even mean its resolution. I'm talking about Colours, viewing angles and the distance between panel and actual glass on the front.
When I saw the 6 for the first time while I was using the 5s as my phone, I was like what have they done to the display, that it's looking sharper than my 5s although both had the same ppi. They reduced the distance between panel and front glass, which made the display looking much sharper.
You can see the same dofference between iPad Air/ iPad 2017 and at least the air 2 or any pro model.
Tend the devices a bit so the speaker grills are headed toward you and you'll see the panel of the air/2017 is much deeper in the device/ further away from the front Glass.
It's like looking through a window into a room where the tv is a bit away from the window itself.
This is what I mean by old technology. Not the resolution.