young, the Bach had it and so did the Or Zarua (a Rishon). We make a Bracha of She’asa Nisim on all eight days. That means that there was a Ness on all eight days. The Gemara explains Chanuka as only because of the Ness of the oil.
The Gemara was actually merely quoting the Megilas Taanis. The Megilas Taanis first says what the Gemara quotes, that Chanuka is because the Menora burned for eight days. Then it goes on to discuss why the Chinuch took eight days. It answers that it simply took that long to fix everything.
The Or Zerua explains that the reason they needed a Ness and couldn’t get fresh oil was because they were preoccupied with repairing the Klei Shareis, as the Megilas Taanis says. He also says that the name Chanuka comes from the fact that they were Mechanech the Mikdash. But the Yom Tov is only a Zecher of the Ness of the oil. “Period.”
By the way, Megilas Taanis was made by Tana’im. By the time the Amora’im came around it was already Batul, besides for Chanuka and Purim.