Clicking a link (discord's approach) is very different from downloading a different piece of software and setting up a new account for each gaming group
You can connect directly to other discord users with no mutual servers. You can make chats and calls with users with no mutual servers. You can make group chats and group calls with users with no mutual servers. You can screenshare in these calls, stream to the group, etc, all just by being Discord users. No need for a server.