Yes, but as gmail has illustrated, that just shifts the problem. Where before your problem was "It got deleted". Now the problem is search pulls up too many things.
Slack seems to be even worse because unlike email, you don't really have subjects or thread beginnings, just continual flow of chatter.
You can make threads in slack. The implementation is a bit weird but (as of last time I used it circa 2018) it did the job sufficiently. For features which required more focused discussion from a sub-team over a longer period of time there was a pseudo-room feature (I don't remember what it's called though)
I don't really have this issue with Gmail. It works a lot better than O365 search with the same amount of mails in it (I recently migrated everything over).
But indeed the lack of organisation of any kind makes it harder for chats.
Slack seems to be even worse because unlike email, you don't really have subjects or thread beginnings, just continual flow of chatter.