Also poorly defined(or explained) power sets.

Elevating/worshiping of king's blood (genetic inheritance, like GOT's Targaryen).

Segregation of of "the same people" to different classes based on the ability to breath.

Tying-in the Roman Empire gives very little time (2k years) between King Atlan to the present day, that's too short a time for inserting Evolution for the species division.

The sinking of Atlantis.... a poor choice/excuse for these hardier "non-humans" to go under-water, if they are already adapted for terrestrial living.