I agree that on the benchmark of time-to-send-a-message, Zulip is slightly slower than Slack, which is in turn slower than just putting the whole company in a W

I agree that on the benchmark of time-to-send-a-message, Zulip is slightly slower than Slack, which is in turn slower than just putting the whole company in a WhatsApp group. But the end goal is not sending messages, the end goal is getting the person who knows about the projector to see your message and respond, for you to see that response, etc. In a moderately sized company, Slack is better than the WhatsApp solution, since you can direct the message at roughly the correct set of people, by spending the extra time to choose a channel. In turn, those people are more likely to get the message in time to act on it, because the message won't be buried under tons of messages meant for other people in the company. Zulip takes that a step further, by adding subject lines to messages. The same tradeoff applies. I think in the end the question really is how much more work it is to add the extra signal. The best case would be you could send messages like in WhatsApp (no subject line, and every message goes to the entire company), and read messages like in Zulip (subject lines, and with channels limiting audience). For both Zulip and Slack, the premise is that we can drive down the cost of adding the extra signal to low enough.