Slack is not a panacea. Sometimes, you need to share a screen and have a fluid discussion, which Slack does not provide.
All-slack communication is definitely not great. It is ok for some communications that can be asynchronous and don't need a support, but that's definitely a small subset of the work communications needed for an engineering context.
Check out slack huddles, they actually work fairly well now.
Was not a fan initially but have grown to like the fairly fluid transition to fully sync comms (for the kind of interaction where I used to go to a co-worker's desk before we were full remote).
Slack is not a panacea. Sometimes, you need to share a screen and have a fluid discussion, which Slack does not provide.
All-slack communication is definitely not great. It is ok for some communications that can be asynchronous and don't need a support, but that's definitely a small subset of the work communications needed for an engineering context.