Exactly. The kind of comment you're replying to is what I expect on a forum where gamers complain about companies not putting content artists on "fixing the servers", not Hacker News.
This. It’s not as if Slack is a tiny startup with three engineers. They’re a large company now of 2,700 or so, with nearly 1,000 working in engineering. At that scale, I am certain they can manage a UX redesign in parallel with any amount of back end engineering required.