Although I don't fully understand the example given, as it sounds like composition to me I will give a disadvantage of OOP
OO is hard to test
No direct access to read/write class variables/attributes - may need to introduce getters and seeters which breaks incapsulation.
Inheritance can change the behavior of a method in a subclass
Objects have state. It can be hard to generate these states as we depend on the public interface.
Classes with loh cohesion can be hard to test as this could mean that the class does more than is specified.
