Just to clarify - I do not claim that learning-roadmap is a great tag. (Although I can imagine that it can be useful sometimes.)

All I am saying that the tag has been around for a long time and I did not notice some objections to the tag. (Maybe this is partially caused by the fact that most MO users do not care about tags.)

Although in this specific case, I should have remembered that this tag has already been added to the question (by me) and later removed (by another user): mathoverflow.net/posts/337533/revisions

SEDE returns this post as the only one where this tag was removed.

Yes you already said it clearly. The problem with meta tags is if they become substitutes to thematic tags. Creating a hierarchy of related meta tags (cf the more frequent reference-request, textbook-recommendation) makes it tempting to use several such tags in questions that have a reasonably precise mathematical subject, at the expense of thematic tags.