Email is crap because there is no agreed on way to structure old and new content, quotes, references and links, everyone insists on bloating with html signatures and crap that isn't part of the discussion.

Additionally, all this bloat and lack of structure makes it hard to search the text for both humans and machines.

Not saying that Slack is better, it addresses some of the structuring and some bloat problems, but adds distraction and encourage discussion bloat instead.