There are definitely several things that I don't like about Slack, but their support has been very responsive. I've reported at least two issues, and they have always taken my input seriously.

A while back, I reported a bug with copy/paste, and they asked questions, acknowledged it, and had it fixed by the next release.

More recently, I had a question about why the UI behaves in a certain way I didn't expect, and they took the time to explain that it was intentional, and what their reasoning was for doing it their way instead of how I expected.

All of these experiences are way better than average for our industry, which in my experience usually just brushes you off without trying to understand your issue and tries to placate you with a non-answer or answer to something other than what you asked.