JTD the pitching moment decrease with the thickness of an airfoil. Tht's how simple it is.
The great challenge in the 50's with the thin wing design and their lack of stability came with that. The video show how the lift center is moving frwd. This move is faster when the thickness ratio decrease. This is why most of the designer during WWII did stick to the 15% ratio.
Supermarine did not have all the viscous flows knowledge as other did and ran straightforward in the thin wing solution (just like the Brits did in WWI). Hence the long dev process. of the Spitfire. That's simple.
Other planes had flaws inherent to their design and did take as long to be fully flaw free.
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