Kubernetes also had (has?) pretty major issues with these, but a community member built some tools using what APIs they do have to make the moderation aspects easier at least: https://github.com/kubernetes-sigs/slack-infra
E.G. Reporting: https://twitter.com/KatharineBerry/status/110594147072323584...
Bulk-Deletion / banning: https://twitter.com/KatharineBerry/status/111310119103288934...
They've been really helpful, but Slack still seems _far_ from ideal for this.