Yeah, the improvements are internal. Many who don’t want to lose the home button or TouchID see this as the main advantage. The new design of the X comes with a lot of unknowns.
I used my IUP for my wife to upgrade her from a 6 to a X. I still could have bought another X for myself with 2-3 weeks shipping that night. The unknowns made me wait. If I want a X I know I can score one without waiting 5-6 weeks, but I may settle for a 8+.