[geofft]

I think you are interpreting the rhetoric as "Slack is not innovative, therefore it is not praiseworthy."

The claim is something else entirely: "Slack is not innovative, therefore it is not immune to competition."

There isn't any value judgment with the second claim. "didn't do anything amazing" is a statement of fact, not a put down. It's not somehow morally bad to do nothing amazing! If anything, it's morally good. There's no sense wasting time building amazing technological breakthroughs when the problem space doesn't need it, and just needs someone to execute well on boring problems. (Slack is particularly good at recognizing this and just getting the job done; see also their tech stack running on PHP.)