So contrary to what you say, the practice of having "alts" is pretty much encouraged.
I don't think you can use the same email on multiple accounts at the same time, but using address extensions or creating new emails is easy.
I doubt any company will tie their hands in perpetuity when it comes to security which is by its nature about ever evolving threats. The number of people who are asking for what you're asking for is simply far too small compared to the number of people who expect companies to fight attackers for them.
> it's simply a demand that I give it any phone number, so this can't possibly serve any account security purpose
The purpose of asking for phone numbers like that is to significantly raise the bar for using networks of compromised / spam accounts. Each number can only be used a small number of times to unlock accounts. After it's used up, you need to use a different number. Thus this forms a challenge that is very easy for virtually all users to pass (they only need a phone number), but is very hard for abusers to pass because they operate at scale. It means they have to find ways to control large quantities of phone numbers which requires either corrupting phone company employees or large spend on SIM cards and special equipment. You can see what's involved in the photos here:
https://www.bleepingcomputer.com/news/security/ukraine-disma...
I mean underlying a lot of Apple stuff is linux. Do you feel you have linux device and its might and endless configurability when working with iphone? My wife can't force that f!@#!@ device to allow her pattern unlock of her phone without losing warranty, Apple rather prefers her having no safety at all (since face ID simply doesn't work for her line of work, and typing minimum 6 digits code 100x a day is extremely annoying... no other choices on 13 mini).
also, the minimum is actually 4 digits. you can tap "passcode options" when setting/changing passcode. not sure how much better that would be though. i generally like face id but i do hope they add in-display touch id sometime.