The PPI required for the "Retina" effect is largely dependent on viewing distance, which is why Apple vary the PPI according to the device, they aren't a blanket ~200 PPI as you suggest.
The Apple Watch and most iPhones (including the original Retina display on the iPhone 4) are around 300-400 PPI, with the X being 458. Only Apple's "Retina" laptop/iMac displays have been around 220, which normally looks great given the increase in the viewing distance.
Wikipedia has a pretty nice breakdown of the PPI of all Retina displays Apple has shipped: