I did upgrade from 7 to X, and you're probably right about the camera. It didn't suck to me but also didn't blow me away. I finally upgraded from X to 12 Pro, and the 12 Pro camera is quite amazing. I just traded the X for a 12 Mini and now using the Mini instead. Equally amazing camera on the 12 Mini, never mind the missing telephoto lens which I rarely use anyway.Dude, the X camera sucks. It was a marginal improvement over the iPhone 7. The X to XS was a much bigger improvement. The XS to 11 Pro was night and day. 11 Pro to 12 Pro is probably like 7 to X.
In the 3yrs I used the X, I never struggled with it using one handed. The 12 Pro is really just a hair taller, but I find it very cumbersome to use one handed. I'm loving the 12 Mini, and will not go bigger again as long as Apple continues with this form factor. Only bad thing is now I have a $1100 paperweight..
BTW I never thought the X was slow, until I got the 12.