The general version of the point doesn’t work very well, and many of the other OO use-cases the author discusses actually work much better than alternatives.
For example, on abstract base classes: if you replace this with a bag of functions I think you end up reinventing virtual dispatch—that is, each function’s top level is a bunch of `if isinstance(...)` branches. This is much harder to read, and harder to add new implementations to, than abstract methods. It’s also no easier to understand.
(There is a subset of this advice that I think does improve your code’s understandability, which is “only ever override abstract methods,” but that is very different from “don’t use OO.”)
For impure classes, the author suggests e.g. using `responses` (an HTTP-level mocking library) instead of encapsulating these behind an interface. This is a fine pattern for simple stuff, but it is not more understandable than a fake interface. The hand-written fake HTTP responses you end up having to write are a lot less readable than a mock implementation of a purpose-built Python interface. (Source: I once mocked a lot of XML-RPC APIs with `responses` before I knew better; it was not understandable.)