I see the author fighting really hard against a paradigm that was already well known to be suboptimal 20 years ago .. "Favor composition over inheritance" is a phrase that became common knowledge in e.g. the Java world half way during the 2000's.
It was even already mentioned in the famous Design Patterns book from the GOF in 1994.
Can't help but wonder if that isn't more the fault of Java's OOP design. Favoring composition over inheritance doesn't seem like something Smalltalkers and Rubyists had to worry as much about.