The implemented solution to this is not very helpful. It was added as a user setting, but most users will not change their settings from the defaults. The issue is that users don't want to spam a channel by joining it, wasting everyone's time, until they know there is content within the channel that interests them. For our users, the join/leave messages serve no purpose and just waste everyone's time. Many of our channels have more join/leave notifications than they have actual content. Please add a global or channel setting to turn these message off instead of just a user setting that few users are likely to even be aware of.

would be very nice for us too

I support this idea, as when MM is used with lots of users (500+), the simple system joining of some channels makes it unreadable.