If 16:9 was perfect then every movie would be shot in 16:9, they aren't.
fwiw, 16:9 came to be as it basically was an average of all the widely used aspect ratios in the 80s :
wiki:
Dr. Kerns H. Powers, a member of the SMPTE Working Group on High-Definition Electronic Production, first proposed the 16:9 (1.77:1) aspect ratio at a time[when?] when nobody was creating 16:9 videos. The popular choices in 1980 were: 1.33:1 (based on television standard's ratio at the time), 1.66:1 (the European "flat" ratio), 1.85:1 (the American "flat" ratio), 2.20:1 (the ratio of 70 mm films and Panavision) and 2.39:1 (the CinemaScope ratio for anamorphicwidescreen films).
Powers cut out rectangles with equal areas, shaped to match each of the popular aspect ratios. When overlapped with their center points aligned, he found that all of those aspect ratio rectangles fit within an outer rectangle with an aspect ratio of 1.77:1 and all of them also covered a smaller common inner rectangle with the same aspect ratio 1.77:1.[1] The value found by Powers is exactly the geometric mean of the extreme aspect ratios, 4:3 (1.33:1) and 2.35:1 (or 64:27, see also 21:9 aspect ratio for more information), √47/15 ≈ 1.770 which is coincidentally close to 16:9 (1.77:1). Applying the same geometric mean technique to 16:9 and 4:3 yields the 14:9 aspect ratio, which is likewise used as a compromise between these ratios.
..but yeah, it's nothing to do with what looked best or what provided optimum viewing of content.. unless by optimum, you mean a ratio for cropping that shows the most amount of average content between all of the other more optimized ratios..
it was a digital compromise
(not that i'm using 'compromise' as a negative there.. 'compromise' can be positive too)
the more recent proposal for a compromising solution with modern content consumption is 18:9 (or 2:1)..
this proposal is attempting to have movies shot natively at 18:9 which is wider than U.S widescreen standard of 1.85:1.. it's wider than 16:9... but narrower than 2.35:1 cinematic..
likewise, it's attempting to have video/TV shot at this ratio too..
16:9 was meant as crop ratio standard.. how to crop the other formats with a common crop..
18:9 is meant as a shooting ratio standard.. how to shoot and present without cropping.. it aims to have less wide movies and wider video.. that's the compromise it's aiming for.
we'll see if it catches on but so far, some modern shows have started using the ratio and, of course, these latest phones are doing it as well.. so it's more than just some hypothetical solution.. we are seeing it being adopted by some of the major players.