You are also comparing two totally different screen technologies...This is a copy and paste/rewording from something I posted in the past about this:
Its kind of like the perceivable audio spectrum.
I've always believed that CD audio was lacking something ("fullness" or "richness") when compared to full spectrum analog sound (e.g., vinyl). I, personally, have clearly heard the difference.
I believe the same concept applies here. Even though one can't see individual pixels above 300 to 400+ PPI, I have noticed a visual richness/fullness nonetheless.
So no, I am not "seeing [pixels] past 400ppi or..." anything like that, but I can tell.
of course oled will look better even if it's the same ppi. Individual pixels can turn completely off. Not something LCD can do. What I imagine is you seeing that. Infinite blacks. Screens pop more because of that. Not the smaller pixels you can't see anyway(past a certain point)