they're two different use cases (for us anyway). we use quip instead of google docs, slack for everything else.
Quip has chatrooms that work like Slack (or IRC, or any other group chat in the history of the Internet).
So what's the different use case?
(I don't see Quip having such an advantage -- although Quip seems like a perfect fit for Microsoft's product portfolio... Hmm...)
Positioning can definitely hurt a product.