Especially voice/video chat, holy crap Slack is ridiculous. The first time I started a Slack voice chat, I actually had time to disable my extensions and log into my router before I figured that no, it's not a problem on my end, it's just that slow and the damn thing loaded.
Slack is just really bad in terms of performance.
- Scrolling up to something that happened fairly far back in history can feel really awkward and broken, image loads and ajax fetches can make the scrollbar behaviour really janky (to be fair, I just tried this and it was better than I remember, although still far from perfect)
- Switching rooms takes about a second, even if I was just in that room, which while not horrible, is still a little laggy for something that should be nearly instant if I have the room's content cached.
Overall while it's gotten better, the "native" Slack app still feels very much like a webpage with OS chrome around it (which is what it is, but other apps like VS Code, Atom, and Discord don't give this impression nearly as much)
This is all on the latest Macbook Pro upgraded as much as possible in every respect save the video card.
Yet, Slack manages to have lag between pressing Enter and showing a message. It's baffling to me how almost nobody doesn't seem to have a problem with that. Miranda IM worked much faster when connected to 6 networks... on a machine that was 10x slower than my phone.
Like, come on.
Can't blame the entire OS for a single program being badly written.
I've a high end workstation on windows 10, and a gigabit jnternet connection. There's no excuse for the delays we see. Another major issue for me at least is their editing system. If you send a message, and edit it "too soon", the UI pretends to edit it, and some seconds later comes back and gives you a modal dialog saying it failed to apply the edit, and undoes your edit. The delay is _huge_ - 10-20 seconds.
Because otherwise I don't really see any inherent performance issues in the problem domain that would require hardware more powerful than what we had in the early 90s. IRC, for all it's UX issues, proves exactly that.