Fawiki is one of the (I think) 2 or 3 wikis that has an "eliminator" group. This group is not sysop, but has the block right. Selection for this group is also not as rigorous as it is for becoming a sysop. The local policy specifically does not allow eliminators to block users who have any of the following rights: sysop, patrol, autopatrol, revert. We enforce this by retrospectively reviewing the logs.
Given T150826, we would like to make it technically impossible for eliminators to block sysops. My initial survey of the code shows this is not a quick fix. Ideas are welcome; my thought right now is to create an extension that (a) defines the "eliminator" role, and (b) calls the rights hooks to prevent the block attempts.