I suspect that any modern force ambushed in a jungle, or any type of complex, unfamiliar terrain, by primitive fighters who know the place like the back of their hands will suffer.

There are stories of UK soldiers in the sixties being ambushed by a man with a scimitar, and it took them a while and several fairly serious injuries before they could line up a shot with their FALs.
Not to forget the Vietnam war which, despite the advanced force being a coalition led by the US, and said coalition resorting to torching the jungle and other war crimes, still ended being up a North Vietnamese victory.

The Endor force, while not outgunned, was maybe outnumbered and definitely outwitted.