Sorry, I'm not ranting, but 50 years of experience should taught you to understand that there are issues with hardware and software that goes beyond our comprehension UNTIL the maker/developer find out and fix it.
If you just type a few words on Google about iphone and wifi connections you'll find a lot of problems, including the one where SOME iPhones does not connect to open wifi with captive portal or another authentication method past wifi connection or with PEAP, like EDUROAM wifi connection through Cisco APs in the university where I work. While most of them work flawlessly, some of them shows annoying behavior, like the one the OP posted here. And Apple simply DO NOTHING ABOUT because just a few users experience these problems.
Iphones are sold everyday, there are millions or billions devices active right now, certainly some have problems, it's absolutely understandable, and if You're counting only a dozen or few more iphones as your experience with them, sorry, but you have seen nothing.
I have to manage more than 1500 devices including - at least - 400 iphones from 5s to 8, owned by students and teachers, and before posting any questions here I try do figure out what's happening and sometimes I succeed in a solution, almost every time with a work around solution or some technical procedure that is hard for users (like to force invalid dns to allow persistent connections to access a captive portal page). Believe me when I say that iphones doesn't work always as expected.
Anyway, I'm not here to compare myself with you. If your iPhone works as expected, fine. I did everything that you posted in your answer in this thread, and more, like explained in my previous answer. If you're disappointed because your advices doesn't work for everyone, sorry, but it doesn't.