I believe that his paper's descriptions of technical advantages of OO are not actually about OO, and instead are about FP and interfaces -- what he calls "service abstractions".
Notice this: when he describes ADTs, he glosses over their power; when he describes the evolution of object code, he glosses over the evolution of interfaces; when he describes messaging, he glosses over protocol endpoints.
IMHO his paper mostly glosses over all the actual technical advantages of OO vs. other approaches, namely OO state encapsulation, OO black boxing, OO inheritance, and OO composition.
He writes that the "key technical characteristic" of OOP is dynamic dispatch, and "is essential to supporting independent, interoperating extensions". OOP's key technical characteristic is not dynamic dispatch -- it's black boxing of data + state + methods. Moreover, dynamic dispatch is not essential to supporting extensions as he claims. To top it off, FP easily does dynamic dispatch by using higher level functions and type classes if you like.