I dislike discord for serious work on a pragmatic level. Every team member is automatically a member of every channel, which is unnecessary and doesn't reflect the needs of even a small company like mine, where there are channels for things like marketing and operations that I, a programmer, don't care about or need to be involved in. Furthermore, and this issue grows as your team does, Discord doesn't have threading. Conversations between 2 or 3 people dominate channels, and if two groups try to have a conversation in the same channel at the same time, it descends into chaos. Sure, you could just tell people to limit conversations to one at a time or make greater use of DMs, but why, in 2018, restrict ourselves to treating text chat like we used to treat radios? The whole advantage of slack is that it's somewhat asynchronous, I can jump into a thread I ignored a few hours ago and concerned parties will see my new message without flooding more recent conversation in the same channel.
To your point, I don't see how fine grained permissions would help with the issue OP points out. Sure, it lets you represent a hierarchy of sorts, but only in terms of what features of the app users are and aren't allowed to use, it doesn't change the nature of the communication.