twisted: The Chanukah neis has nothing to do with the Hasmoneans subsequent rulership. Indeed Chazal are critical of the Hasmonean for taking the reigns of power since they were Kohanim not Davidians. Additionally, the bad behavior of the Hasmonean rulers were of later generation Hasmoneans not the ones that defeated the Yevonim.
From the Rambam Laws of Chanukah (and yes, even though they did other things wrong as you correctly point out, the reason for the holiday is ????? ????? ?????? ??? ?? ?????? ???)
???? ??? ?????? ????, ???? ?????? ?? ?????, ?????? ???, ??? ????? ???? ????? ????? ???????; ????? ??? ??????, ?????????; ?????? ?????, ????? ?? ?????, ?????? ??????. ??? ??? ?????? ???? ??????, ?????? ??? ????, ?? ????? ????? ????? ???????, ??????? ????. ????? ??? ??????? ??????? ???????, ?????? ??????? ????? ????; ??????? ??? ?? ???????, ????? ????? ?????? ??? ?? ?????? ???–?? ?????? ????