>>but as you can see clearly from the megillah, organizing an army for defense was NOT the method the Jews took nor would it have worked.
You see the exact oppisite from the Megilah! They did organize an army! As the posuk says
נִקְהֲל֨וּ הַיְּהוּדִ֜ים בְּעָרֵיהֶ֗ם בְּכׇל־מְדִינוֹת֙ הַמֶּ֣לֶךְ אֲחַשְׁוֵר֔וֹשׁ לִשְׁלֹ֣חַ יָ֔ד
בִּמְבַקְשֵׁ֖י רָֽעָתָ֑ם It was not the first line of defense but they certainly did do so when they were able to. As Chazal say the parsha of Yaakov and Esav in V’Yislach is meant to be a lesson for doros that we use three methods tefilah, doron and milchoma when dealing with their threats.