One thing I am seeing here is an extension of the meaning of political corruption beyond that found in the dictionary. Here is what the Oxford Dictionary writes:
Other dictionaries may include illegal behavior as well in the definition.
Note that the meaning of corruption does not include unequal access to power by the rich, if that unequal access is neither dishonest nor frauduent. Unequal access is an issue separate from corruption. Trying to eliminate corruption when conflating it with unequal access confuses the two issues and makes dealing with either of them harder.