Samsung's OLED screens look excellent (assuming you get one with good unjformity), but two things need to happen for OLED panels to overtake IPS LCD entirely:
-Full RGB displays. Pentile is a waste of CPU/GPU resources for a less than advertised resolution.
-Stop using PWM (flicker) dimming. Its irritating to the eyes and it makes the display visibly unstable at <50% brightness.
Despite popular opinion, color calibration is no longer an issue (assuming you use the basic color profile).
Better yet, get micro-LED production going and skip OLED enitrely. Less burn-in concerns, at least in theory.
On the flip side, resolution doesn't matter past 300ppi on a smart phone. Can you see any pixels during normal use of your iPhone? If not (and you can't), there's no reason to get a higher resolution display.
I generally agree with your post, but i wanted to mention a couple situations where >300 ppi actually does have an impact:
-Very small text is more readable on the OLED screens. Generally you only see this on desktop sites, but I've heard that Asian characters are also more readable (they tend to have very small details).
-Extremely high physical pixel density allows you to render any LOWER resolution on the display without visible loss of quality. What I mean is:
720 rendered on 1080 screen looks much worse than a native 720 display because of antialiasing blur...
BUT 720 rendered on a 4k screen is virtually indistinguishable from a native 720 display because the AA can be done at 4k resolution. There's very little cost to high res full screen AA.
So a super high PPI display allows you to get high quality at any resolution, letting the user decide between increased fidelity and lower lower power usage.