There are lots of these. Are there “ancient relics that are so advanced they should not exist” or, quite simply, all surviving ancient technological artifacts were completely within the technological capabilities of the people who created them?

Of course if they were not within the technological capabilities of the people who created them, they would not exist. Artifacts may change our modern perceptions of what ancient peoples were capable of, but, if an artifact exists and it is genuine, then we can surely say with any measure of integrity that it should exist!