I don't really feel like reading all that just to figure it out.
Did you resolve both of the issues brought up by OP or not?
(Answering: "The password policy was added to Team Edition back in June, 2018.", isn't the same as answering, "the free tier allows passwords of length >5 characters.")
1) Enforcing password requirements for end users was put in free tier last year - Here's why, with a link on how to use it: https://github.com/mattermost/mattermost-server/issues/5935#...
2) Non-admins are still able to archive channels they belong to but did not create - Here's why: https://github.com/mattermost/mattermost-server/issues/6320#...
3) I need to work on speaking more concisely, here is another version of #2 from an HN user who puts things more simply: https://news.ycombinator.com/item?id=21824219
Does this help?
I'd love for there to be a viable alternative to slack that is more (if not entirely) open.