Grammatically, "with all due respect" is interpreted as an insult because it questions what is due, whereas, Respectfully, is seen are respect for the person addressed. I will assume you meant the latter, not the former.
As for whether the was used for science in Ancient Egypt, or it was just cut up is not a huge field to find an answer. As for how long it takes to comprehend Ancient Egypt and mummification, I would say that depends on the person; their drive, their free time, and their intellect. Never judge another by one's own life. I happen to be that person who can and does find time to do what I desire. Doing what one wants is a choice, after all.