What it was "optimized for" is irrelevant if it's legible and has good information. The mpv manual read in a web browser is both of those. The VLC manual is a mediawiki (if we're talking about subjective appearances, mediawiki has always been fugly) that's both sparse and out of date. Changes to mpv make it into the manual because they're both in the same repo and people making changes to the code are expected by community convention to have the corresponding updates to the manual in their pull request. This doesn't happen with VLC.
The only upside of the VLC manual is that only one in a thousand VLC users will ever need to look at it in the first place. mpv's manual is necessary but high quality, while VLC's manual is low quality but extraneous.