I've seen questions such as Why can't I flag some answers as very low quality? and understand that it's probably by-design that one cannot flag an upvoted answer as Low Quality.
However, it's not uncommon to run into posts that don't seem to meet the site standards. (I've often heard that link-only answers aren't encouraged.) But if a post has been upvoted, you can't flag it low-quality. I know I could still flag it for moderator attention but having it landed up in VLQ might ease up mod's tasks a bit in such cases.
For example, the following answer:
(the revision history holds more fun).
I'd rather refrain from citing examples in this post but strongly feel that an upvoted post doesn't imply that it's not of low quality.
There should exist a system to flag it such.
EDIT: For somebody like me who prefers to flag low-quality answers, it's not uncommon to have those marked Disputed. Amusingly, it's often observed that those answers with now Disputed flags are deleted by the mods. Those do affect the flag statistics.