So if you use Discord right you could more or less recreate Subreddits inside a single Discord server.

I am part of some Discord servers that utilizes this. Downside is that it doesn't have comment threads which might be one of the things that made Reddit popular. Also, because Discord is more meant to use for chatting, people type a lot of non-productive stuff that you have to go through instead of filtering from top/best comments. Servers that have slow mode turned on (can only send a message every # of mins) to help still has this issue as well.