He was great. How about that fight against  Jess Willard in 1919
Yes it is known as the worse beating in boxing willard suffered many broken bones
I read that he toughened his hands with horse urine and developed speed by racing against horse wagon teems
True, He use to travel under trains with no food and fight 5 times in 2 weeks he was really poor , so poor if he didn't win the fight he didn't eat so he literally had to fight to eat 
How do you think he compares to Mike Tyson and Muhammed Ali at the top of all their careers
Well i can tell you this... He was one of the boxers who inspired Mike Tyson 
Have you read Roger Kahn's book on Dempsey?
No i have not but i have watched a lot of documentaries about him
Well I highly recommend the book A Flame of Pure Fire as you so much like Dempsey. You will really enjoy it
I will be sure to check that out