The tags answers-in-comments and answers-as-comments seem to refer to exactly the same thing: comments that should be answers. Because of that, answers-in-comments should be made a synonym of answers-as-comments. It should not be the other way around because answers-in-comments has a lot less questions and no tag wiki.
"Answers as comments" seems ambiguous to me. Does it mean "answers being used as comments" (the content is a comment, but the post is an answer post) or does it mean "answers posted as comments" (the content is an answer, but the post is a comment post)? Both interpretations seem equally plausible.