Earlier quoted context omitted.
As far as I know, all the pieces to make Slack have been around for a while. But nobody ever put them together properly. So the fact that all the pieces existed doesn't count for very much in the end. Nor was it obvious that if someone put it together properly it would achieve commercial success. I was theoretically in the right place at the right time to have put together something like Slack at my job, but there wa…
What people are saying is that not only have the pieces to make Slack been around for awhile, but IRC has implemented those pieces successfully for 20 years. The only "innovation" Slack provided was the UI, and that's textbook "bad startup idea", because of how easy it is for someone else to step into the space.
It did indeed... implement them as pieces. The out-of-the-box experience for an IRC network does not look like Slack.
And the UI was a non-trivial component. Personally I'm in the segment who doesn't much care and for whom IRC is a fine amount of bandwidth... but a looooot of other people, including lots of people with money, want something more.
Slack is not "just IRC". The proof is that if it was, we wouldn't be talking about Slack, we'd be talking about IRC. We aren't.