In Teams you can just call the first person up and then add more people into the call. "Jane Doe is calling you from a group chat" or whatever it says. I'm surprised this is a new-ish feature in Slack?
It's hard to explain. You're in a channel already, e.g. your team's channel, and you hit a toggle and it creates a voice chat and others are notified to join. I think it's really slick.
Teams has that too, you can call groups, or teams, people can pop in and out at will.
Two years ago the multinational company I was working at had a global ransomware attack and we had a teams call for like 7 days straight with check-ins every two hours for everyone but there were on call people in there always if you had specific questions.
It worked really well and made it easy for people to get stuff done and have clear chain of command when everything else was down.
I know what you mean - we had Teams at my past place. Difference is Teams UI is intrusive, which might suit command and control style orgs. Huddles are much less intrusive. You can do regular calls with Slack as well, Teams-style, but huddles are much slicker IMO.