A 27 inch 1440p monitor has a PPI of ~108. These are what all high end consumer displays like the Apple Cinema displays, Dell U2711s, etc had before they all moved to 4K.

A 27 inch at 4k has a PPI of ~163. This is basically industry standard for high end consumer displays. Sure there are a few 5K screens, but they are not common. I've also seen a lot of folks use 32 inch 4k displays which would have even lower PPI.

A 15 inch 1080p screen has a PPI of ~146. So not as good as a 4K screen at 27 inches, but still MUCH higher than the 1440p monitors.

Nope. 1080p has enough pixels to display most text nicely.

No. I specifically buy laptops with 1080p displays and avoid hidpi if possible due to compatibility with various apps, as well as power consumption/battery life issues. I have a hidpi MacBook for work and a 1080p System76 machine for personal use, and I vastly prefer the System76 machine.

I accept that others see it differently, but I have this lingering suspicion that the whole hidpi movement is mostly marketing. Most folks simply don't need it, or even really benefit from it, as far as I've been able to tell.

That's all nice but from my experience when you go outside the common 1080p 60fps stuff starts to break in funny ways even on windows. Heck, I have a 1080p 144hz display and while scrolling on most stuff is super smooth and 100% worth the premium( or the sacrifice from going with a TN panel), it's also really blocky in some apps.