Without seeing the original Q it's kind of hard to judge this individual case, but here's my general view:
I think it's good practice to downvote what you think is a bad answer. Regardless of the nature of the question.
If you really think the answer makes the original work worse, by all means downvote and leave a comment saying just that. Maybe substantiate a bit why you think the work is worse.
If you really want to step it up a notch you can invite the user(s) to The Looking Glass or a private chat to discuss their works and what you think makes them better or worse.
EDIT after OP linked to original Q:
Since the question is five years old I don't think there is much impact still to be had. The user was last active four years ago, so I don't think they would mind losing 2 rep to a downvote. The OP has probably moved on, the logo is either in use or it isn't. Nevertheless, the above still stands: downvote, comment, leave it.