Preparation is not about spending the most money - its like saying that 00's startups were way more prepared than nowaday's companies. No they only foolishly blew more resources.
A great general (or businessman for that matter) needs to have a knowledge of art, history, psychology, rhetorics, economics, philosophy and lastly military strategy (and also needs to be physically fit). That is what Sun Tzu really teaches. Being well rounded in all life's aspects gives one sufficient power to rise to any challenge.
Not some brutish spending of money and lives. Be it war or business.
As Sun Tzu said: It is best to win without fighting. And if we return to the French - they could have won WW2 without fight - if their deluded politicians wouldn't load Germans with unfulfillable liabilities.
What I have read of his work does make much sense - but is dangerous when taken out of context of his vast military experience - which is exactly what happened - what we have seen in western Europe from mid 19th century and culminating in WWI was predominantly fueled by Von Clausevitz's work. His delusion was trying to present his subjective life's experience in a scientific and absolute manner. And what happened was that people took his work and applied it literally.
I'd say it's more subtle than that: the side which is more appropriately prepared always wins. Arguably the French were "more prepared" for WWII if you go by amount of effort expended - building the Maginot line wasn't cheap - but it didn't do them much good.