My two cents is that if they didn't have Discord, they would just find other outlets for their behaviour. Discord has made some of these behaviours a whole lot easier, like you said, but it's not as if they weren't even there before.

One thing I want so say is that although I'm sure some people let the shitpost chatting distract them from actually posting, I do feel that sometimes that chatting can help encourage activity by letting people feel less like a pack of strangers that happened to have mashed together for some RP. Sort of like a huge ice breaker.

Also, in the latest RP Discord that I've joined, we seem to have done well enough segregating the "important information" areas from the "shitpost" ones, so it's usually easy enough to find what you need to know without having to sift through 100 messages of nonsense.