This is a fair criticism, but IRC is decades old while Matrix is what, 3-5 years old? Give it time and choice of clients and servers will only improve.
IRC is a joke once you’re used to Slack, especially in an organization that uses it well.
Naturally, how each of us feels about that experience is subjective. So setting that aside, the part about IRC that I haven't seen handled with Slack is being a one-stop shop. With IRC, I can discover and access multiple communities within a single server at once. The most popular servers can be connected to and browsed with a click in most IRC applications. With Slack, I need to find a project's Slack workspace, request an invitation, then go through the process of adding it to each of my clients. I'd love to see the equivalent of a FreeNode workspace where I can join an OCaml channel and a Ruby channel without going through all of the above and dealing with walled-off communities.
Revisiting resource consumption, I've opted out of communities that moved to Slack because once I hit around 10 workspaces, the Slack app slowed to a crawl and guzzled RAM. To be fair, that's gotten a lot better in recent years, but I still find managing several workspaces to just be too much cognitive overhead. I may only be in one channel on each workspace, but I can't easily switch between them. With IRC, doing a "/join ##ocaml" is super fast, barely consumes additional resources, and adds a new tab to my main interface for fast switching between channels.
I know about IRC bouncers and all that, but I don't want to set up a server just for that, and managing them is a pain as well. I know about IRCCloud too, but I don't use chat often enough to justify $5/month (I'm poor, and I just want to chat occasionally).
I don't care much for Slack for many reasons, but at least I can actually use it. I find IRC to be functionally unusable because of this.
From a quick glance, it looks IRCv3 solves this with the chathistory extension/specification.[1] But AFAIK most (no?) servers implement this (yet) and the specification isn't finished either.
I'd also add that I've often seen IRCCloud banned from many channels due to extreme amount of spam from their users.
There are Slack gateways that exist for native applications. I currently use a Slack libpurple plugin with Pidgin, and although threading is slightly cumbersome, eliminating Electron and/or a browser has greatly improved my experience overall.
Slack is a product
There is a really big difference
Burn Slack to the ground is my considered stance at this point.
- messages sent to you while logged out are lost
- no support for videos, images and GIFs
- (usually) not great support for emoji
- no support for file attachments
- no useful mobile clients unless with support from the server
Yes, those can be considered frivolous features, but they are used by people to express themselves (which is, in essence, what a chat protocol is used for), they are expected because IRC's competition has them, and some of them are an objective usability improvement that I'm not willing to go back on.
The advantage of doing it this way actually makes it easier to scroll back in the chat history when you're searching for something that was posted.