If this is really a low-priority item, wouldn't it make sense for the help page to say something like, "If you are editing an article and find an obsolete HTML tag, of course it is OK to replace it, but eventually bots will be created to replace obsolete HTML tags, so there is no need to edit articles for the primary purpose of replacing HTML tags.
Topic on Help talk:Lint errors/obsolete-tag
Funnily enough, there is a somewhat similar guide / help that does something like that in the parent page (Help:Extension:Linter#Goal: HTML5 output compliance). Adding it in the help here probably won't help much. Clearly it seems likely that you have missed it in the parent page, others will probably ignore this page altogether. It is just human nature.
In any event, since this is a wiki, one can act accordingly (improve it if need be).
U:Anomalocaris, let me add it to the help page so others aren't confused similarly.