OK, you are right. . . But it is not a change in PPI on the iPhone 7 plus. The iPhone 6 Plus, and the iPhone 6S plus have been 401 PPI since they were introduced, because that is the way the numbers at that size and screen work out to be. It is the 1080 resolution available at 5.5" diagonal. So what? It is still the same Retina display that has been beating the pants off all the Android phones out there that are claiming huge numbers of PPIs.
Is 326 PPI all you need, or is 401 PPI better? Why would Apple offer both - unless there was a visible difference with the higher PPI (and thus making your own, earlier position about 326 PPI is all you need a mistake)? NOTE: Apple offers both resolutions, why is that?
As far as beating the pants off of Android phones, again - you're going by biased reports. If you look at an independent, scientific measurement based review, you find the following:
The Galaxy S7 matches or breaks new records in Smartphone display performance for: Highest Absolute Color Accuracy (1.5 JNCD), Highest Peak Brightness (855 nits), Highest Contrast Rating in Ambient Light (186), Highest Screen Resolution (2560x1440), Highest (infinite) Contrast Ratio, and Smallest Brightness Variation with Viewing Angle (28 percent). In addition, almost every display lab test and measurement shows some improvements compared to the Galaxy S6. See the main Display Shoot-Out Comparison Table for all of the measurements and details.
The Galaxy S7 and Galaxy Note 5 are neck-and-neck record holders for display performance, effectively tied or alternating between first and second place in almost all categories except screen size for the much larger Galaxy Note 5, and the much higher pixels per inch for the Galaxy S7. What is especially impressive is that the overall display specs and performance of the Galaxy S7 have been maintained or improved after being scaled down by 20 percent in area from the Galaxy Note 5. So… as the result of its even higher ppi, the Galaxy S7 becomes the Best Performing Smartphone Display that we have ever tested.
Record breaking. The Best Performing Smartphone Display they have ever tested (and that includes the iPhone 6 variants). It's not Apple - it's Samsung.