Homer was a poet first...
Hi ER
I think it was a real conflict, but in the broader context of Mycenean raids on "Hittite"/Anatolian city-states over an extended time. Basically the "Greeks" were pirates akin to all the Norse who went "a-viking" each year when weather permitted. I suspect the Anatolian city-states had suffered some reversals and the pirates just added a straw to the camel's back. Illium was just one victim of a pretty brutal bunch of piratical rulers. Homer knew a lot of stories and, chronology permitting, knew some very old veterans.