You can type @ before a username to send a notification to another user, or even just type the username. For example, you would type '@brian' or 'brian' to notify myself. This could be done on a message board, as that's a feature over at The Annex TM, but MT doesn't have anything like that. I honestly, get a lot of misdirected notifications, since Brian is a fairly common name, but it's still a nice feature.
I do understand that it can be a struggle to read everything that's posted on Slack, and I honestly, don't think it's intended for that. I had a hard time adjusting to it at first, and I did decide that I wouldn't use it, but then I noticed that a lot of people over there don't post here much at all, so I went back, and I've grown to like the pace of it. Sometimes, though, I just have to mark things as read. Sometimes, it is a bit frustrating knowing that I'm missing a lot of good Twin Peaks discussion, but the reality is that even on a message board, I'll miss a lot of discussion simply by virtue of being busy with other things. I do also like that it's more in the moment, and the use of reactions is something I miss a lot on MT.
On a side note, another reason why I don't really like to use this message board right now is that when I just clicked to view "New Content," nearly every thread was spam of some kind. I know Jonathan has promised to fix that, but it's desperately needed.