How is Discord superior to Slack?
The voice channels are flawless, even when there's people on shitty internet connections.
The client is always responsive and snappy.
Their design of how the server/chat/voice/videos/users is laid out is is clearer, easier to see what's going on at a glance and it manages to do that while it fits more information on screen.
Their dark mode is much better.
Their code display/highlighting is better.
The user groups/roles which is more like tags is much better than others.
It's way easier to find where notifications come from.
Yikes, here's hoping you mean "after a year" or something, because having to make a fake new thread just to comment on an existing locked thread would make me rage quit
Someone with the manage threads permission can unarchive it, but like the pinning thing that also comes with permission to delete it, so you can't just grant that to everyone in your server.
Auto-archived threads automatically unarchive themselves when you send a new message. Locked-threads, on the other hand, require explicit unlock.
Slack does app integrations and bots pretty well.
To give an example, let's say you have both a Discord channel and a Slack channel with the same 10 people working on a project, 7 of which are software developers. To mention the developers, your Slack option is either @everyone (including 3 non-developers) or individually. On Discord you can create @developers and add only those seven, not bothering the other 3.
You can really go buckwild with that basic concept: only admin can tag @everyone, only @talkers can join a voice channel, only @projectmanagers can run some bot, only @collaborators can post to #project, @watchers can read #project but not post, while those that are neither @collaborators nor @watchers don't even see the channel... And in #otherproject you can have those same people in totally different groups and with different roles.
Way more customizable than by just having public/private channels and @everyone at your disposal, as Slack does.
And some other features like colours which are nice when you want mods to stand out for public servers, or teams for some sort of competitive event server.