We got the chog with its 20mm why not the F6F with a perked option of the 20MM.
Have you not been reading the thread?
The only F6Fs that used the 20mm cannon operationally (-5N and -5P) are variants that aren't in the game, and the standard F6F was never equipped with 20mm cannon outside a handful of test machines.
The F4U-1C WAS used operationally.