I've heard this theory a few times but I'm not so sure. From the docs and articles I've read men were always the dominant ones.
The 3 docs (one involving a french doc maker, the other a few aussie men looking for gold and a very old D. Attenborough film) I've watched about PNG tribes who have either very limited or no contact with the outside world showed nothing in terms of equality. The men were always the ones meeting the strangers and trying to communicate with them, the women were barely involved if ever. In the aussie doc the natives were ''trading'' very young girls with the white men for sea shells.
Then there's the articles about the uncontacted Amazon tribes, a few photos from a few years ago showed men pointing their bows at the plane circling them... no women in site. Or the tribe on a small island south on India where no contact is believed to have been made : the men shout and throw spears at any approaching boats, no women in sight once more.
I mean, it seems to me like these men were as aggressive and dominant as ever. I read somewhere that Marx was one of the people who came up with the idea of this gender equal pre-agricultural paradise. I don't know if that's true or not but then again he was a fucking moron so I wouldn't be surprised. 