For me it looks like this is only a presentation issue on Special:RevisionDelete. When using "Hide target and parameters" and after that going to Special:Log the user name is still visible, while the presentation on Special:RevisionDelete indicates the user name is also hidden, because it is striked-through together with the action text. But the action text and the user name are in the same system message (user is only a parameter), but the user name is not hidden on other pages. So making a own user field seems to be complicated when also showing the unhidden content.