First things first, not FOSS, not federated, phone number requirement, VPN hostile, therefore bad. Pedos, MAPs, groomers, razor sharp edgy kids.

Now we come to a more non ideological analysis.

• For my OSINT investigations, Discord is fantastic. This is simply because it is a mainstream platform, and mainstream platforms are necessary evils. This is a use case hardly anybody has or should have, as it is a risky and tactical task.
• The trifecta of Reddit, Discord and Telegram has pretty much taken over forums and boards, as it stands.
• Discord works as a public forum exactly the same way as Telegram does, except it is a massive honeypot. A little careful observation tells all media is stored on Google Cloud, when a message is deleted. Telegram is incomparably superior to Discord despite having similar stances on privacy, security and anonymity, simply due to track record.
• Discord is a public forum, therefore it is not meant to be private, secure or anonymous as far as message content or metadata goes. The privacy comes from how secretive a guild ("server") itself is from masses, and what kind of content it hosts that will attract particular kind of users. The security comes from centralisation and 2FA via phone number, so impersonation attacks become insanely hard, unlike on pseudonymous, anonymous, or federated platforms.