You are right.
Although, I am not sure too much of the media does go too far with it - it's not like its an all pervasive myth. I don't think there's that many real examples of journalists etc trying to claim that big dicks are more masculine.
It's more to do with implications, in things like movie costumes etc.
I have known men with small dicks who were very masculine in other ways.
And men with very big ones, who were really quite effeminate in some ways.
It really doesn't link that well. And that's how it should be ... it would be boring if you could always tell how someone might behave just by looking at part of them.
What does masculinity really mean, anyway ? I think it's about truth, objectivity. Simplicity. Engineering.
Not so much about power. A lot of power is held by women, I truly believe. Even though some of them don't know that, or understand it, or use it properly ...