I really don't agree with the main thrust here at all, and I think I agree with the analyses the OP was trying to rebut: it basically boiled down to luck. There were other viable (and even better) chat products out there.

Lacking a "reply" feature almost kept me from using Slack. It is still the only new feature I want in Slack. I would trade half of the integrations (I mean, Giphy sucks, it really does, and the Hangouts integration is just a race condition with an icon) to have that one thing.