The benefit of one big app is a consistent identity. Seeing that an account was created years ago, and how long it's been a member of the current server, helps identify spam and scams. When a user you're familiar with provides a link to another Discord server, its more trustworthy.

Discord has also done a good job protecting identity; better than DNS has :) I use lots of other apps with "real" identity, Discord is good for centralizing non-work, non-family activity.