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On top of that, they have things that are considered "Enterprise Ready"

I'd be curious to hear some numbers on the percentage of active users with Nitro subscriptions. Slack's business model makes it easier for them to make monthly revenue off passive users (by encouraging teams/companies to over-provision and also double-dipping in the user overlaps between teams/companies), so in some respects it incentivizes them to optimize for passive users. The Nitro/Server Boost business model is likely to have fewer passive users paying the subscription costs recurring monthly and doesn't as easily double/triple dip users (unless they intentionally and optionally overpay for server boosts), but it incentivizes the company to keep active users happy.

Slack is also thin, supports third party clients and is super easy to code for (Discord is too, but more hoops). And provides actual enterprise worthy support. From a professional POV deciding between both is a no brainer IMO