Did Israel already have organization before Jethro's advice?
Yes. The people already possessed a functioning order when they left Egypt, coming out with their armies and a relatively good tribal system, not as a disorganized rabble. Jethro’s counsel later proposed appointing able men as rulers over thousands, hundreds, and fifties, but it did not create Israel’s initial organization.
Les explains that when Israel came out of Egypt, they already had organization; they came out with their armies and were not just a bunch of rabble. They already had a relatively good system by tribes. Jethro advised Moses to teach ordinances and laws, and to provide able men who fear God, men of truth who hate covetousness, placing them as rulers of thousands, hundreds, and fifties. Yet Les stresses that the chapter never says “and the Lord said”; the Lord is out of the picture. This is strictly a man speaking in the energy of the flesh, even though it sounds logical. Moses, the spiritual man in close relationship with his God, harkened to his father-in-law, the pagan Midianite priest, and did all that he said, picking out men.