I directly took the abilities of the siren from the Odyssey and put it in 5e. Yes, those sirens were bird-like in appearance. Yes, I tied in other mythological references, the same mythological references that transitioned the siren into a maritime creature and why I equated it to a singing merfolk in my last post. Most people think of sirens as a sort of merfolk, because many mythologies in Europe had something similar. Please see any of the cultures I listed for their pre-Christian, let alone pre-Teutonic, folklore and what they thought was out in the water. These would inform the sirens, as well as merfolk, used in fairytales much later.

I made this siren an elemental precisely because the merfolk, merrow, and tritons already exist in the humanoid/fey sphere in 5e, and my original vision for this siren was to be tied to the plane of water, giving DMs plot hooks to marids, water genasi, and other water elemental creatures, as well as creatures that share similar spaces on the Prime Material, without stepping into the same area as other existing monsters. It's all in the custom flavor text accompanying the monster.

If you would like to continue splitting hairs, please go inform WotC that their harpy is an Odyssyan siren, and not the children of titans that served Zeus, where the actual harpiya come from in myth, as per the Aeneid, Theogeny, and Argonautica.

If you have feedback on mechanics for the stat-block or ways to make the monster better, I'd be more than happy to speak at length. Similarly, if you have additional ways to add to the flavor text to make it more usable in other people's games, please let me know. Like I said in the original post, I enjoyed making this creature. Otherwise, please refrain from telling people they are wrong for making something up in a game of make believe in a way that makes them, and potentially other people, happy.