I struggle to see where Slack is spending all of that money. It's a chat application with a few million active users at any given time. Even with absurd AWS bills, they should still be raking in profits.
So long as retention is good, and your unit economics are profitable, it is like running those dollars into a money-printing press by buying an annuity that will pay out for years.
Instead, the rule is more like: is CaC sufficiently lower than Customer Lifetime Value so that each customer is profitable. This ratio tells you if your money-printing machine is working. As the low-hanging leads dry up, CaC gets higher.
Your argument might be rephrased as "their customer lifetime may be shorter than they think." Possible. There's some amount of switching cost (lost history, webhooks and integrations) there, though.
In terms of competition, we've seen plenty of alternative pop up recently such as Mattermost and MS Teams, both of which have gained popularity.
In terms of consumption, it is only feasible to really have a single chat application at a time, maybe two if one is being tested. Having more than 1 defeats the purpose of having an org wide chat. Maybe individual teams will choose their own in large companies, but the general assumption is you try and sell your chat solution to the company, not to the individuals. And so we have a situation where the presence of strong competition directly effects the consumption of the product (Slack's offering).
My opinion is that Slack was previously somewhat synonymous with company chat, but that is no longer the case. They peaked, and now that Discord, MS Teams, Mattermost, etc. are viable alternatives, their market saturation is on the decline. They let their grasp slip away, and they will pay for it.
Slack has still had a net gain in users in the time that those competitors have gained users as well though, right? If everyone is gaining users, that seems like a reasonable argument against the market being saturated.
I know you're talking about within an organization, but this made me realize how long it's been since I've used a client like Pidgin/Adium/bitlbee that could handle multiple chat protocols all from one client.
I'm pretty sure the majority of the protocols I used to use in these apps aren't even around anymore (other than irc and xmpp).
Pinterest looks to have earned about $1.1 billion in revenue during the same time with roughly the same number of employees. Fastly is at $250MM in revenue with just 630 employees.
So it looks like Slack is at least twice as large as it should be for its given revenue. But why? Are they supporting too many platforms/devices? Or are chat applications just not that valuable to companies?
What do they do? I am curious on the breakdown of engineering versus everybody else. I am always reminded of Craigslist, which operates with a skeleton crew. In 2017, it was reported they had 50 people on revenue of almost $700 million.
Before that, they spent a significant amount of time and resources on the new WYSIWYG editor that was extremely unpopular and caused them to do a public 180 after saying they wouldn't go back.
In short, it's being wasted on sour grapes and untested ideas.