Discord works well in practice for creating groups and channels. By default, regular users cannot create channels. Like Slack, it has very fast search, with no message limit. File and image upload work wonderfully and the audio/video works every time.

For small-scale groups, Group DMs are fine, though, I would warn to try to use Group DMs only for when more than two participants should get an urgent ping on a message. (Users can "mute" group DMs so they don't get notified by them.)

The problem with group DMs in slack is that they are almost always better off as a channel - you can’t really add new people to a group DM. So you’re forced to decide if you should make a channel or not right at the beginning.

Group DMs can also have usability problems, and they tend to clog up the UI of slack. I currently have 5 or 6 group DMs going that all have at least one of the same people in all of them, so now when I use the quick switcher I see all of those. Some of them even have 2 of the same people in them - it makes it really easy to select the wrong group.