I don't distinguish between a root post and a post with a parent, in terms of functionality. The consensus logic does not either, and I think it used to.

Yes, I think you can say that a comment is an upvote/downvote on the content, absolutely. As you can read in my rather scattered writings during my Dawn period, I even think you can skip voting altogether if you count a view as a vote, also, and confirm that with a share, which affirms that you believe the content is worth consuming.