Sefar herself is based on the fish god paintings in Tassili n'Ajjer, Sahara. It is more likely for her to be related to African deities. Surtr also has certain similarities to her with his abilities. The reason that you can link her to the Olympians is because they are currently the pantheon we knew the most about. We literally got information about their entire myth within 2 chapters. Meanwhile we barely knew anything about other pantheons, especially their origins. Once we learned all about other pantheons and they don't have any mention to her, that's when your suspicion would make a bit of sense.
Except that she cannot be reasoned with, like Tamamo said. Even if you're down on the knee begging, the titan will still curbstomp you. That's why the case of Mesopotamia gods managed to form a contract that they will help her one time in exchange for her not fighting them was a special case and we still don't know how they managed to do it.Perhaps she only defeated Olympians and every other Pantheon just resigned seeing that they don't stand a chance (being equal in power to Olympians).
And again, Vasavi Shakti exists, Tiamat exists but was sealed away long b4 Sefar arrives, Chaos was also always there. So it's not that they have zero chance, they just did not go that far. Vasavi Shakti was probably created a bit too late in the war and the holy sword beat the titan before it was finished, the Mesopotamian gods probably didn't want to take the risk of using Tiamat to fight Sefar which will wipe the planet clean regardless (beside, asking mommy for help after sealing her away for ages is not a good idea), and the Olympians did not want to merge or let Chaos into this dimension.
Nope. They are literally just using their functions as machines to manipulate the environment. Their mechanical functions are "close to be equivalence to Authorities". Because they are not embodiment of natures like the native gods of Earth, they have to substitute Authorities with their functions. The Olympians at that time did not "abandon their material bodies to become one with nature" like a lot of gods from other pantheons. They did not become concepts with True Ether bodies, but they were still products of an alien technology and civilization, thus they still could not escape Sefar's bullshit.I am pretty sure that at that point even the Mecha-Gods came to embody different aspects of Earth's nature like they do in the 5th Lostbelt.