History preservation is not just about continued existence, but also about discoverability. Other forms of communication (issues, project planners, and email lists) are much better for the latter.
I honestly don't even see the argument for why this is true of email lists. I went from an email-list-heavy environment to a slack-heavy environment, and both have been pretty equally good/bad for this.
I do think issues, project planners, design documents, etc. are better for discoverability, but they are also, in my experience, far less complete a history of what's been going on, than whatever the primary communications platform is.
There has been a lot of useful work that gets done in the cracks between the planning and work tracking artifacts, every place I have worked. I think you can either make that persistent and discoverable, despite it being super noisy, or just lose all the context on it altogether.
