My concern with OLED is burn-in, which has happened to ALL of my Android phones, including the ones that had displays that the manufacturer, and the net, and forum users said would not. With the iPhone, this would be a huge "do not buy" red flag for me, as there is no message notification LED, requiring that I leave the display on all the time while plugged in, so I don't miss messages. Combined with the color shift over the course of the year in all OLED displays, from blue to yellow, the forum here would be a cluster for years, of never-ending threads about OLED issues. I have LCD devices over 10 years old that still look as good as when they were new. ALL of my OLED devices look like puke now.
I don't know. I've had 6 samsung phones and never had this issue. I don't have any experience with other android phones.
Older OLED do have some issues. But newer OLED have improved.