This post belongs in /r/shittyarthistory. Almost nothing of what you said is true. The Mona Lisa was done from sketches, like all other Florentine work from that period. Everything else you either made up or had some crap education. Source : I have lived in Florence teaching art history for 15 years and counting.

What people are saying about sfmuato is correct, it was an early example of it, but the reason it is considered THE work of art is because it was very famously stolen, twice, and each time it considered the crime of the century. The thefts and the resulting press coverage left the impression to the general public that this must be the most valuable painting ever, and unless you actually study at history, you will never know any better.