Apologies I misread the initial post when I replied, I thought OP was saying the XR replacement this time would get OLED.
My take...
What is now the XR will become the smaller device if they go down that route, with the “lesser” camera.
The Pro models will then be the two larger devices with better screens and cameras, especially if they all have OLED as otherwise the Pro model with the same screen and slightly better camera wouldn’t be enough difference from what is the XR now is in the range.
So the regular iPhone is the smaller device then the Pro then the larger Pro.
But who knows, I genuinely hope they do make a smaller device again. I have an SE now and just sold my XR as it was too big, something in between those two without a massive price would be very popular, but it’s Apple - so who knows