There are some other interesting implications from centralizing it like that, too. For example, clients who communicate using Slack Connect are unlikely to be retaining their own independent records of the communication. This potentially puts them at a disadvantage in the event of a contract dispute. They may be unable to obtain a record of past communication without resorting to a legal discovery process, and you need to lawyer up and file a lawsuit before you can do that.

With email, on the other hand, retaining one's own copy of the communication is baked into how the mechanism works.