The part where you said for most people 4.7" is enough. The sales of the XR says otherwise. 6.1" is the limit based on sales.
As mentioned above, there was no smaller option to the XR so that means nothing. I get what you’re saying, but had the SE and XR released at the same time with matched specs the SE would have taken a lot of the sales when prices below the XR.
The 8 wasn’t an option to anyone who wanted anything with modern specs in comparison to the XS and XR.