Maybe it just comes down to what we are use to. My company has optimized slack with our systems and we have specific guidelines on how to use it and ensure good communication. So it is very smooth communication and integration. I find it to be a much better tool and like MIMH I find email to be an old system.If it's in a personal message and not a channel, using Teams for long messages with attachments is dumb. Especially if it's somebody you message frequently. Sure, you can try to remember a keyword and search or go through a list of files to find what you need, but let's not pretend like that's an efficient way to work. You might prefer all of your communication in one place but again, that doesn't mean that it's the best tool for every form of communication.
I agree that channels better than DMs for most things. That is the one thing that search function fails at with slack "was that message wit these 4 people or these 5 people"? But we have guidelines on this to prevent this from happening often.
