I find it hard to believe that Slack etc would increase my productivity.
Of course if you're only optimizing for your single productivity measured in lines of code written then I can see your point, but software engineering at scale is a team sport, and Slack has traits that make it better than email/in-person discussion/phone/zoom/in-doc comment thread.
You'd think, until your org. decides to deploy a 2-3 month retention window on all slack content because of legal concerns.
I'm completely sold on decisions being driven by a doc of a few paragraphs with the conversation around it co-located in the comments. It's easy to scroll through a list of such conversations in the message board and read through the context with discussion. In comparison, finding a previous conversation is slack is much more difficult.
Even if I can find the conversation, I think that the chat-focused nature of slack encourages short, loosely worded messages. This is great in the moment but the lack of context a few months on is pretty tough to deal with.