A number of people have already attacked one of your fundamental assumptions about low skilled labor. I think one way to say it is you're making the assumption that what you call "low skilled labor" is in fact "zero skill labor." I think you underestimate the level of skill required to deliver goods efficiently and quickly, and yes, the cost that is involved in it. (to be fair, you seem to be saying that I am overestimating that skill in your first sentence.)

Also, "one off consumers. Varying routes every day." Well, delivery company employees will have precisely fewer of those because their job is to deliver things, seems like the reason not to trust Amazon drivers over Fedex.