Yes, I totally agree. I think there are a constellation of factors that influence the upgrade decisions of users, but I have found it surprising how much the software has been under-discussed following Apple's miss.
If someone was happy enough with their iPhone 5s, 6, or 6s running iOS 11 when the X was released (Fall 2017) then I suspect they didn't feel much more pressure to upgrade when they were running iOS 12 and the Xs was released (Fall 2018).
If someone was happy enough with their iPhone 5s, 6, or 6s running iOS 11 when the X was released (Fall 2017) then I suspect they didn't feel much more pressure to upgrade when they were running iOS 12 and the Xs was released (Fall 2018).