I see it as a kind of "chicken and egg" situation.
Being in a position of high power can certainly expand an already inflated ego (I lived with such a case for 17 years; eventually got a craw-full of it.
But if you come equipped with a rampant case of over-the-top narcissism, that is not likely to slow your race to the top.
Whichever comes first, it is likely to help the other.
The article says the effect can be combated by people in power not surrounding themselves with yes men, and having people who will call them on their faults. So much for the GAs.
At least there’s a psychological basis for their lack of compassion.