if i were writing an intro to programming book, i would introduce OO as a means of building encapsulation. i'd only get into inheritance in later chapters.
It's pretty much the definition of OOP.
The core feature of OOP is just bundling functions with the state it processes.
When you bundle state and functions together, you can't predict what calling the function will do without knowing both the code and state.
You can say its 'the real benefit', I guess, but that feels like circular reasoning. Its pretty much the definition of what OOP is, so calling it a benefit feels weird.
Unfortunately, designing systems as a collection of distributed state machines tends to become maintenance nightmare. Functions and data being separated tends to make code better, even when working in so-called 'OOP' languages.
It's a benefit compared to how people were writing code before it became mainstream (for polymorphism: by jumping to data-defined parts of the code and hoping for the best, and for encapsulation: subroutines working on global variables).