IMO, the only way that WhatsApp could even compete with the value created by Slack would be by giving away the product to its international user base. And on to

IMO, the only way that WhatsApp could even compete with the value created by Slack would be by giving away the product to its international user base. And on top of that, you'd have to assume that the same user base is too lazy to download a free app for their phone, which I think is pretty safe to assume isn't the case in the slightest.