About Matrix Matrix is an open protocol for decentralised, secure communications.
Matrix Manifesto We believe:
People should have full control over their own communication. People should not be locked into centralised communication silos, but instead be free to pick who they choose to host their communication without limiting who they can reach. The ability to converse securely and privately is a basic human right. Communication should be available to everyone as a free and open, unencumbered, standard and global network.
Yes, you can have 1:1 and rooms on Discord too, but the level of customization of rooms, roles and permissions Discord has is much more advanced than what you can find in WA, Telegram or Matrix.org.
On Discord when you’re in a server you can see (usually) every other user that’s on the same server, and in every room you’ll see some of those people, depending on the permissions. That’s not how the other options mentioned before work.
Also, on Discord you can have specific rooms dedicated to audio/video chats, on the rest (WA, Telegram, Matrix) it works differently.
I think it’s mainly because of those reasons that people compare Matrix to WA and/or Telegram instead of saying it’s a “Discord alternative”.