Their response, courtesy of Paladox, a staff member, is the following:
"Hi, thank you for asking that! Our official position is that we respect all comments and opinions regardless of intent."
We recommend users file feature / bug reports since that is how Miraheze will improve!"
Basically, there is no need to be afraid of criticizing Miraheze as a service nor criticizing wikis here, though I recommend we add a limit that such criticism must be with reason (aka "Miraheze has issues with occasional server load" is reasonable, while "Miraheze is a crappy service because they suck" is not)
Any technical complaints we or other wikis notice should obviously be filed on Phabricator, but criticism of their service or wikis on it here is not something we should be afraid of, unlike other wiki hosting services, they believe transparency is a good thing.
With your permission, I'd like to amend policy in light of this, and draw up a provisional page for the Miraheze service in general.