An Amaroutian in one quest discusses the use of a 'matrix' to store his proposed creation and it is well established the complex entities like Carbuncle and Eos are generated using crystals, said to be ideal for 'data storage'. It could very well be that Creation magic beyond short lived conjuration was once beyond ancient humanity as well...is there any solid indication the unsundered Ascians were empowered by Zodiark? If so, Emet's recreation of Amarout on the ocean floor might not be a good metric for what the average Ancient was capable of achieving with their own two hands and nothing else.