A Chinese example of this for me is Jin Yong, probably the most influential wuxia (Chinese martial-arts fiction) novelist in the Chinese-speaking world. His books are popular fiction in the most literal sense: enormously entertaining, widely read, and for many people first encountered simply as page turners.
As a kid, that was how I read them too.
Only after I started working did I realize how perceptive some of the character writing was. Murong Fu, for example, is genuinely capable, but his ambition is even greater. Everyone around him, friends, followers, even people who love him, is ultimately someone he is willing to sacrifice for his goal. I have met people who seem to reproduce almost the whole arc: the ambition, the triumphs, the disappointments, the pain, the struggle, and sometimes even the madness. Suddenly Murong Fu no longer feels like an exaggerated fictional character.
The book never changes. I had finally acquired the experience to see what was already there. That feels like thickness to me.