Is this not misleading due to the screen width of the iPhone 6/7/8 being the same as the X? So if you watch a movie which isn't stretched to fit then that dimension will be the limiting factor. 16:9 ratio content will look the same size even on the larger X as it does on the 6/7/8 - except you get more black space at the ends, or you expand content, lose top and bottom and gain a notch? While the phone itself is larger in every dimension and quite a bit heavier. It doesn't seem you're gaining a great deal for all the flash (and cost) with the X.
16:9 content will always be better on 6/7/8.. regular or plus models.
that's because the screens themselves are 16:9..
also, old movies or tv shows will generally be better on phones prior to iPhone X (the closer you get to a square aspect ratio, the better it will be on iPhone Plus vs iPhone X.. regular sized iPhones will be moreorless equal to the X as far as physical size of content appearing on the screen)
most (by far) movies are shot wider than 16:9 and they'll adapt the the X better.. especially the real wide movies like the Wonder Woman example.. (meaning- they'll adapt better to iPhone X if compared to any previous iPhone)
where the X (and other recent elongated phones such as S8) will really shine is with the modern format of 18:9.. (or 2:1).. it seems these phones were built with that ratio in mind.. many of today's 'prestige' TV shows are shot this way like House of Cards, Transparent, Stranger Things, Fargo, etc.
for example, here's Stranger Things on iPhone X:
..it fits perfectly in between the notch and the margin on the other end.
in other words, iPhone X is to 18:9 as 8+ is to 16:9..
or, the ratio of the X appears to be built perfectly around this ratio.. it will perform better with cinema movies and worse with 16:9 content..
whereas previous phones are built perfectly around 16:9 ratio.. except they perform worse with 18:9 and even worse again with cinema.
if you only watch 16:9 or squarer, then the previous phones will fare better with these sizes..
if you're viewing more modern content, these new style phones are more versatile and you'll always be getting a better view with them.. and the occasional worse view when going back to something more square.