This article is much the same if we replace “Discord” with “GitHub”, for instance, or “Twitter” or “YouTube”.
There is a fundamental difference between what they listed as one though: GitHub and YouTube are open to read and access and download and clone. Discord and Twitter are not.
I have much more of an issue with Discord than I have with GitHub or YouTube. Both GitHub and YouTube have free access, and host the largest part of the relevant userbase (synergy effect of having an account).
It's certainly worth discussing in project teams, but personally, I'd never leave GitHub in the current ecosystem for a niche product or platform - if I want contributors and collaborators or visibility. The vast majority of users already know GitHub and most accounts are on GitHub. That can't be said for niche platforms or self-hosted alternatives, which introduce barriers.
Before GitHub Sourceforge was somewhat similar. It was a proprietary but open platform. In a project I participated in (Mumble) it was reasonable enough (no more complicated than between any other platforms) to make the switch to GitHub. I see todays GitHub the same way. As long as it remains so primary prevalent and open to free access it's good enough, and when it goes downhill it's easy enough to switch away to a better alternative.
I'm still fond of alternative FOSS platforms, that they exist and evolve, and maybe easier account creation, synchronization, or federation will make them real alternatives. But for now, they are niche. Which of course doesn't mean niche is unviable or an alternative. But even as an invested and interested FOSS developer, user, and collaborator they're barriers to me. Which makes it obvious to me it's even moreso for less invested people.