After saving Tom Thumb’s life Jumbo’s legend grew. He is at least 15 feet tall in the eyes of Tufts students - that is the benefit afforded those who live a life such as his. Nameless Mammoths are afforded no such benefit.
If you want to refute Barnum’s claim, then the burden of proof is on you - The skeletons are available for the measuring.
The Mammoth was not lean - it had large fatty deposits that served as an adaptation against the cold…
(By the way, the genetic sequencing of the Mammoth was probably performed on equipment invented by Tufts)
http://www.reuters.com/article/us-science-mammoths-idUSKCN0PC2LZ20150702
In fact, the Mammoths pointy head (and resulting extra height) is the result of a big fat deposit! 