I agree with the publishing of the bans, but I am not sure Wiki (and specifically Mediawiki) is the best place because, as correctly noted, the wiki infrastructure ensures the information is preserved forever. While in theory everything public on the internet is forever, in practice there might be benefits to not carrying old grudges around.
The problem to solve here is not statistics though. It's nice, but it's a different case. What is really needed is when action is in force, I (as a participant of the collaborative platform) can see that it is, and adjust workflows accordingly. It is a collaborative environment, so the ban would affect collaboration. Aggregated report is useless for this case - if I worked with X and their account suddenly shows up as "disabled", it won't help me any that in 2 months time I'd see in aggregated report "number of bans: 7". What I need to know is: a) was X banned? and b) for how long. Most community members, I suspect, would also want c) by whom and d) for what.
I am not sure how it can be possible that the ban won't be public - account being disabled on Phabricator is pretty public, and we'd be kidding ourselves if we ignore the fact that this is what people would assume (especially now). If we do it in non-transparent way, people would just assume more and create a narrative in their heads which might not necessary be even true, but is inevitable. I do not think the fact of the ban in a public collaborative platform can be hidden. Or should be. We might not disclose any details about it beyond the duration (I think this is a must), though I would advise in general case not involving sensitive matters to opt to more disclosure (again, secrecy breeds mistrust, and mistrust makes people construct narratives that we'd want to avoid). But I do not see how hiding bans is practical, or desirable.