Re: The main benefits of Outlook
What that means is that Legacy protocols, IMAP and Activesync particularly but also the likes of POP3 and some weird Exchange/Exchange online endpoints bypass "Modern Authentication" so you can't enforce MFA on them, either via Conditional access or by hard-enabling it. Password spray / brute force attacks pretty much all use these protocols which can't be fixed without changing 'the protocol spec' which everyone would moan about.
Instead, sensible IT departments turn them off at the Organisation level to help the department sleep safe at night.