My 2.5 year old LG G2 is full HD (1920x1080). Gak.
iPhone7 -- 5.5" 1980x1080
A 5.5" LG G4 is 2560x1440. Gak. Gak.
Why? 538 PPI resolution is almost TWICE the resolution that the human eye can discern at normal viewing distances on that size screen, and FOUR TIMES the number of pixels necessary to be invisible to the human eye with normal 20/20 vision. So why bother to put so many pixels on a device of that size? It's a ridiculous waste of resources and slows down the responsiveness of the device!
The BEST a human eye with 20/20 vision can discern at 10-12 inches is 1 arc second, or 278 PPI. The iPhone's lowest resolution is 326 PPI, far beyond that threshold, which is equivalent to 0.74 arc second, good enough for anyone with 20/15 vision, which only 7% of the population can see. Your 538 PPI resolution is a ridiculous waste of hardware, memory, and bandwidth. It requires too much system resources just to push pixels around the screen for absolutely ZERO discernible user benefit. It's only there for marketing hype.
This is one of the reasons why the Apple iPhones have been consistently beating the pants off of every Android phone in benchmarks and real world speed test. Apple equips its iPhones with exactly what the user needs to optimize the user experience while being able to move the screen at the best speeds for animation.
Having excess pixels in the same area, pixels the which human eye cannot discern, pixels which are NOT a benefit, is NOT something to brag about when their mere existence majorly degrades the performance of the device, nonsporting.
A 4k Ultra High Definition 27 inch computer monitor has only 157 PPI, but it is more than sufficient to be called a Retina display because it is intended to be viewed at approximately 20" to 24" from the user. A 4k 55" Ultra High Definition Television, the state of the art, has only 96 PPI, again because of the distance one views it. In a digital movie theater, with a 35 foot wide screen, the digital image is still at best only a 4K digital image, the resolution is 11 PPI, yet to the audience it still seems sharp and clear.
“My 2.5 year old LG G2 is full HD (1920x1080). Gak.”
1080P at that screen size is enough that the pixels vanish. Thus, “Retina display”. Higher res screens do nothing but sell phones to the gullible, with no tangible benefit. In fact, graphics performance suffers as the benchmarks clearly show.
This is one of many areas where Apple is getting it right.