The Facts are quite easy, and confirmed by the insight book, under "Assyria". The 70 years of Jeremiah 25 indeed started at the 17th year of Nabopalassar, when he defeated the Assyrians in Haran. That is where they became the supreme power of the region and one after the other of the "surrounding nations" became vassal, or under servitude, of Babylon. The former supreme power was Assyria. It is telling you do not find this tidbit of info under "Babylon" in the it-book. A comprehensive list of the vassal nations you find in the 2nd part of Jeremiah 25, e.g. Elam = part of present day Iran. As the territory of all these surrounding nations is immensely vast, obviouly they did not become vassal nations at the same time, it required some time to bring the Babylonian armies to the nations. That, the by then sill crownprince, Nebuchadnezzar needed some time, estimated 4 years, to bring also Judah into this servitude, does not influence the starting point of the prophecy.
Face the Facts, Rolf Furuli tried the very same thing with the same kind of words as you do. His book did not convince anybody.
Hoffnung