Anything above 400 DPI or so IS quite worthless, you CANNOT tell the difference in actual use (you barely can above 300 DPI). And DPI is NOT the main reason these new iPhone screens are so good. ACCURATE (not just bright-but-wrong) color and great viewing angles are much more important.
The iPhone 6 Plus renders (most?) content much higher than the 401 DPI, and that overage IS worthless, even harmful, in many ways. (It's useful for software reasons, allowing developers to have 3x assets.) Luckily, the 6+ still delivers great battery life and real-world speed even so. Not a deal-breaker, then. But, if it were not rendering those wasteful pixels, it would be EVEN faster and run EVEN longer. These are the engineering trade-offs that someone had to decide on. As an Apple fan, I wish no such trade-off had been needed. (I certainly don't wish the Plus had more than 1080p pixels burning battery.) I don't think you'll find Apple fans denying these facts exist, though. You may be seeking a strawman...
Note: one reason you CAN benefit from even higher DPI on many Android devices: they use low-quality OLED "Pentile" displays which have an ugly checkerboard effect. The checkerboard is TWICE the size of the pixels. So if "real" RGB pixels (used in better screens like Apple's) become invisible by 400 DPI, it make sense that Pentile might show the checkerboard defect (kind of a diagonal "screen door effect") up to much higher DPI. Higher DPI hides the problem better. So, by choosing poor but cheap Pentile displays, Android-handset engineers have their own performance- and battery-sucking trade-offs to face. Even the upcoming flagship Note 4 retains this cheap display compromise supposedly, hard as it is to believe.