Auld Soul,
I won't disagree with your line of reasoning , however, it appears to me from reading Exodus Ch. 18 that Jethro had become a believer in the God of Moses prior to making his organizational recommendation.
Exodus 18:9 Jethro was delighted to hear about all the good things the LORD had done for Israel in rescuing them from the hand of the Egyptians. 10 He said, "Praise be to the LORD, who rescued you from the hand of the Egyptians and of Pharaoh, and who rescued the people from the hand of the Egyptians. 11 Now I know that the LORD is greater than all other gods, for he did this to those who had treated Israel arrogantly." 12 Then Jethro, Moses' father-in-law, brought a burnt offering and other sacrifices to God, and Aaron came with all the elders of Israel to eat bread with Moses' father-in-law in the presence of God.
It was after these events that Jethro watch Moses and provided his suggestion.
Exodus 18: 13 The next day Moses took his seat to serve as judge for the people, and they stood around him from morning till evening. 14 When his father-in-law saw all that Moses was doing for the people, he said, "What is this you are doing for the people? Why do you alone sit as judge, while all these people stand around you from morning till evening?"
15 Moses answered him, "Because the people come to me to seek God's will. 16 Whenever they have a dispute, it is brought to me, and I decide between the parties and inform them of God's decrees and laws."
17 Moses' father-in-law replied, "What you are doing is not good. 18 You and these people who come to you will only wear yourselves out. The work is too heavy for you; you cannot handle it alone. 19 Listen now to me and I will give you some advice, and may God be with you.
I don't see where Jethro was saying that God wasn't able to accomplish his purposes but rather it sounds as if Jethro is saying that Moses wasn't handling his responsibilities correctly or judiciously. Perhaps Jethro already knew of Moses penchant for pride?