Amazon doesn't have any competitors? They are literally Walmart or Target + leasing access to their IT infrastructure. Name one thing that isn't AWS that doesn't overlap with Target/Walmart. And AWS literally maps to Walmart IT and Target IT, they just aren't interested in competing in that space (and rightly so).

As for AD: An email address isn't an identity. I'm not sure why you would expect the two to match. I don't login to my mac with [email protected], I don't expect to login to my Windows laptop with [email protected] either.

The searching I can only surmise you were doing it wrong? I've never had an issue searching by first or last name in any tool whether it be the AD tools themselves or Outlook.

AD is a directory server, it can service a Windows environment or a Mac environment or a Linux environment. They've got a complete implementation of LDAP if you choose not to use AD auth on the client side. That being said: EVERYONE integrates with AD. Very few people integrate with anything else. I like having unified auth in my environment, perhaps you enjoy managing local hosts but that sounds disgusting to me.