Flagging would be an abuse of another feature. I don't think the original post is quite wrong as in illegal or harmful or off topic.

The commenter here's upvote counted, my downvote did not count.

And I won't just use any other available form of attack like falsely accusing the post of some wrongdoing just because I want to criticise something and that's the only way to do it.

I did leave a critical comment but that is a seperate issue because you can leave a positive comment and upvote. So the ability to comment nulls out.