This seems like a reasonable approach when all actors are being paid to contribute.
I think where discord actually ends up helping is for community projects where everyone is basically a volunteer. It works because it lowers the barrier to helping.
The official documentation of your favorite programming language or highly popular library or framework is probably pretty locked down with a semi high quality bar for contributions. This is a good thing, those docs are consumed by lots of people and the documentation has no context for what the person is trying to do so making sure they are clear, concise, and easy to understand creates a high quality bar.
A lot of projects end up with enthusiastic helpers who probably aren’t going to dedicate the time and energy it takes to become a core maintainer. You can either leave these people and their possible helpfulness on the table or you can harness it with a discord server.
People that might not be the right fit for writing an in-depth general purpose getting started guide are still pretty great at answering peoples questions when given context and the ability to discuss it back and forth. That’s what projects are actually taking advantage of, a large group of people that are willing to help others learn how to use the programming language / library / framework.
The people they help end up having a good time with the friendly helpful community and hang out and help others. If you do it right you get this virtuous cycle where people using the thing you made help each other be successful making the thing you made even more popular.
RTFM, is ok in a corporate environment when part of your paycheck is for RTFMing. But for the last 70 years people that know how stuff works have been shouting RTFM at people wanting to learn how stuff works. But some people just aren’t good at RTFM or plain don’t want to. Discord, and other chat platforms, end up facilitating their learning models.