If you think SSO and easy profile migration doesn’t save time, there’s simply no point in discussing it with you. I don’t like MS and their near monopoly position as a company much either. But that doesn’t mean every product they make is utter trash for every situation.
There are undoubtedly other solutions but to pretend every one is too dumb to use them shows how little actual experience working in a variety of companies is.
Back in the nineties you might have had Novell NetWare or just plain old LDAP instead of AD, but unlike those competitors AD kept working and offered upgrade trajectories. And it offered decent integration with a decent mailserver (that ofcourse sucked to set up securely for outside access), and that mailserver was fantastic versus the utterly terror that was Domino combined with Notes. I don’t like MS for basically forcing you to go to their cloud now, but pretending it’s a bad product through and through on a functional level is just being willingly blind.
And your arguments have the strength of the hobbyist with the homelab he’s constantly having to reinstall, not understanding why companies are so stupid to not do the same thing as him.