As soon as the author claimed IRC was a competitor to Discord or Skype I had to stop reading.
Case in point.. I used to run game servers for maybe over 1000+ guilds over the years I was active. Even talking 10 years ago, people were still using Skype for connecting to games... just because it doesn't fit your use-case doesn't mean the market wasn't competing.
IRC was also in the space. Look at the dozens+ IRC servers which had communities built around them... they've mostly migrated to Discord.
I'd love to know your counter point to such an absolute-claim though... because I positively agree with the author.
Elm lang has an IRC channel. Like all IRC channels on Freenode, it's pretty much dead. One reason being that only a small fraction of people even are willing to use IRC, mostly because they're old enough to know wtf it is.
But then the Elm creator started a Slack server. ...And it's absolutely bustling. There's people getting help. There's people giving help. There's people golfing code or discussing design ideas. There's people sharing their projects and receiving feedback. There's different channels. There's people meeting people and making friends. There's people sending messages to offline users and offline users able to read them when they come back online. And there's even people posting multiline code snippets, something that tends to come in handy for a software project of all things.
There's people who want to grow an online community, they tend to discover Discord very quickly. No brainer. And then there's people who want to convince an increasingly empty room that the application layer protocol behind the community is what matters most.
10 years from now, Discord will be gone but IRC will remain.
These days I prefer Matrix, but I have no doubt IRC will stay around. Maybe even because of Matrix users like myself who just keep bridging it in.
On the other hand, in 10 years if Discord pulls the plug, you'll have a community of people that can migrate elsewhere. To any other solution that will pop up. Because it's the people that are the community, not the platform. Whether I have to use Discord or Slack or future solutions is merely incidental and entirely swappable.
One example that comes to mind is https://thedonald.win/. Reddit killed their subreddit (r/the_donald), so they just moved elsewhere.