An interesting difference between Twitter and Discord is legibility. This is not a new idea but seemed worth exploring in more detail.
(I can't actually find the original source for the Discord connection so I'll just vaguely gesture at Venkatesh Rao's map post and say it's probably somewhere in the social graph around his Twitter account.)
Twitter is a platform of the legible social. Twitter gives you an explicit social graph: Jon follows Sally follows George; Moxie also follows Sally. Besides that, it gives you a closely related implicit and easy to navigate graph in terms of replies, plus a few more graphs for good measures via lists, likes (maybe?), and retweets. Really there are a lot of graphs. These graph structures make the social connections easier to understand without needing to closely follow anyone's conversations or reason about them.
Following the structure this way is easy. A computer could do this. Computers have done this.
Meanwhile, Discord seems designed not to be legible. Individual users do not have account pages where you can read their every message. There are no follows or lists. Discord has a reply feature, but it doesn't make a comprehensive record of a conversation, because people frequently don't use it. They don't have to; they are implicitly replying to one of the last few messages in the thread or channel. This is often good enough for the immediate conversational purpose. Many conversations don't need to be found. Furthermore, Discord allows near arbitrary 'sharding.' Every community is its own private-by-default bubble, and the visible social graph doesn't tend to follow you across those, making user activity less legible. Furthermore, there are I think often smaller private Discords behind any large public one. These are completely illegible to anyone not in the server – unless someone tells you that one exists, you don't even know you're missing something.
I've once or twice read people complaining about it being hard to find things in a Discord. Maybe this is a feature and not a bug.
This only goes so far. Twitter has DMs. These are an illegible part of the social graph. I'm not sure how to factor this in, because I don't have a Twitter and don't know anything about DMs or how they are used in that context. It seems worth noting as going against this pattern.