e621 has minimum quality standards, and if new posts do not meet those standards the moderators will remove them.

However, I don't see an option to flag existing art as low quality so it can be removed.

I would recommend the art from the artist gs-leal be removed. It's low-quality art from over a decade ago. The only art maybe worth keeping is the latest one.

If it's not yet been approved, you can flag it as not meeting the uploading guidelines. Moderators will otherwise take care of it when they're looking to approve posts. If a post is already approved, a moderator has already determined it meets the standards.

aaronfranke said:
I would recommend the art from the artist gs-leal be removed. It's low-quality art from over a decade ago. The only art maybe worth keeping is the latest one.

Old content from before the rules changed is grandfathered in, and not deleted under the new rules unless there's something seriously wrong (e.g. it's showing something illegal).

As Watsit said, old art is grandfathered. Already approved posts should meet the quality standards, since either a janitor had a look at them already, or they were uploaded by a user with unrestricted uploads, they should know what the quality standards are. However, humans make mistakes. Therefore, the flag reason "Does not meet the uploading guidelines" is now unlocked for priv+ for already approved posts.