I saw the post (and with everyone else here felt some horror at the idea that MU is dead) but didn't realise I could discuss it here until now... :-)

Long and short - we use it all the time. We actually use it for mini-app building (WordPress is kind of perfect for this with out-of-the-box auth, theming, functions, etc) - multisite lets you throw up a new part of an app really easily, so /client1 /client2 - all with custom front ends.

I also run another business, https://themuseumplatform.com/, which is built entirely on top of multisite. The fact we can spin up a new instance for a client with a core set of themes, plugins and functionalities in seconds is a huge, huge boon. Yes, it'd be "easy" with WordPress single site, just not nearly as flexible or simple...