The community does have systems to handle such situations though (e.g. the arbitration committee which has produced this letter).
Of course, these systems may or may not be adequate - I am not qualified to say, but it seems to me that the chief complaint here is that the WMF did not involve any community systems without having previously expressed concerns about them.
This suggests that either the WMF does not consider the systems adequate, in which case the arbitration committee is quite right to request that the WMF communicate this to them, or the WMF has some genuinely top-secret reason to ban someone that even the arbitration committee cannot be trusted with (which for a matter as light as a 1-year ban due to community reports doesn't seem likely).