One of Slack's greatest missed opportunities IMO was to become the hub for every company's customer/advocate community. Once you've established yourself as a customer service channel and internal coordination hub, you're deep in the operations of the company. They already had the brand cachet, they had everything going for them.

And if they were worried about abuse, or about cutting into their B2B bottom line, they could still do things like "users who spend less than X minutes a month browsing/posting, and join only community-visible channels, are considered community tier" so that employees who spend more than that (or even who want to have a single private DM) are still charged. And have a generous nonprofit/open-source/startup-accelerator program.

But by forcing every company to treat every active user as a fully licensed user, they ceded the community space to Discord entirely, an unforced error that likely lost them an entire generation or more of customers.