In my mind the biggest minus for slack is that we are on the free plan, which has several drawbacks, the most impactful being that only 10k messages are being kept.
I archive them periodically, so it does not get completely lost, but its not great.
I have been thinking if we could come up with some automation, e.g. Slack -> GitHub Discussions, but unfortunately afaik the gh discussions API is kinda meh still.