> most people who hate Slack are probably using it because their org says so, and their org doesn't think it sucks

I agree in part but you are underestimating the power of inertia. A lot of organizations use Slack because they use Slack. Moving from Slack to something else is a headache. The OP could build an objectively better product than Slack by every single measure as accepted by every single stakeholder in a business, and still not take business away from Slack.

The current positioning is probably the best for right now. The people launching new startups who don’t love Slack might come across Dock and the pitch may resonate. As a mature product with thousands of paying customers, positioning as “Slack that doesn’t suck” won’t work to steal away Slack’s customers and Dock will need to mature their positioning, but that’s a future challenge for a different stage in growth.