I don't think that's an inherent notion of Discord at all, although it is a case of poor defaults. I turn on most of the muting settings immediately when I join a new server (notify for: nothing, suppress @everyone and all role @mentions, etc). Throughout the day, I'll mainly click between the 2-3 servers I actually care about, and every few days I'll go through some of the others. New messages are still marked once I click in so I know where I left off, pings are still highlighted so they catch my eye as I'm scrolling through, but if I don't care about a conversation in a channel, I can just scroll to the bottom and it's all immediately marked as "read."