The OP does make a few valid points, particularly around screen size for watching videos and the side button. I know screen size is based on diagonal measurement, but the the extra width on the plus model is very noticeable.
I switched back to my 8+ after about 6 months with the X. Here were my main reasons, which is my own personal opinion specific to my usage:
1) Screen Size (as OP mentioned) - I watch a lot of videos on my device, and it is my primary source of media consumption (with a toddler at home, TV is off limits for most hours of the day).
2) Battery - The OLED screen consumes a lot more power when being used continuously. While the results with the X weren't bad, they pale in comparison to the Plus.
3) Status Bar - This was the one thing that constantly bugged me, personally, when using the X. While I admit that it is a bit trivial, I like to be able to see the time and battery status at the top of whatever app I'm using.
4) Multitasking - I found this to not really work that well for me. Whenever I tried to switch apps by swiping the bottom of the screen, it would only work about half the time. I guess it is just muscle memory, but I am so familiar with the home button double press it is fluid for me.... again, just my opinion.
There are 2 things I do really miss from the X:
1) Face ID - I never had any problems with this in all my time using the phone. It was so fluid and natural from day 1.
2) Tap to Wake - Having already been used to this from my Apple Watch, this feature that was a nice touch. Being able to check the screen without having to press the side or home button, was surprisingly useful.
All this being said, I am really looking forward to the X+ coming out later this year. Issue numbers 1 & 2 are addressed by the phone itself. I am holding out hope that issue 3 will be solved in future software iterations (or possibly the phone itself with the extra screen real estate), and I have no doubt issue 4 will be fixed in software updates (or by finding out that I am just an idiot and am doing it wrong).