Hi! Creator here (of iOS404) - you can filter level of standard and compare to FF Android (or compare to Safari Desktop, or any mix) instead if you'd like.
There are 34 features listed (IIRC it did contain a bunch of Chrome-only crap once upon the time, hence my harsh reaction). All of them enabled by default. If we limit this only to actual, you know, standards, and not "scribbled on a napkin, awaits review", we get a grand total of 9 (yes, nine). And even there many are not "not implemented" but "missing some features (sometimes big, sometimes small and irrelevant)".
I've had real-world experiences where I develop something that works on my Mac and my Pixel phone but cannot work on iOS WebKit (basically kaputt on iPhones). It inspired the creation of the site - specifically not being able to allow users to have Audio at anything but 100% seemed extremely weird.
I'm not offended by sites that also point out issues with a slant against Google. Ie: killedbygoogle - I think these things are great, fun, and interesting.