AOA - Sir, you have just done the same thing. While he posted numerous pilot records about slats, you choose one from a single book as a proof...
Is the book reliable in all aspects? Does the author really understand aerodynamics? Now I don't have the book in my place, so I can't check it, but it seems to me that this is one I've actually read and there were several mistakes caused by authors misunderstanding of how things work and were designed.
It sort of reminds me a book by Stephen Bungay who was trying to mathematically prove that the 8 machine guns of a spit/hurry were more effective than 2 cannons of Bf-109 E...
Now to your quote - "...Less experienced pilots could put a Bf 109 into a stall and spin when the slats deployed on one wing and not the other in a tight turn..." Sir,
Less experienced pilots is the key here. It means they ignored the warning the slats had given them and continued pulling on the stick
... It was mistake of a pilot not a plane... and less experienced pilots avoided near stall conditions at all... and it and it has been reported many times...
World would be a better place if we listened to each other instead of shouting...
And THE QUESTION about slats has both answers actually
- they do both in logical sequence...