Barnes very rarely guards PFs. If anything Green and Bogut trade defensive assignments as was often the case in the Memphis series.
And Iguodala has always been a ball handler/facilitator throughout his career. The Warriors definitely do have a couple players that are swiss army knives in Iguodala and Green but I still wouldn't say they are a positionless team. Again, Doug Christie, Webber and Vlade all handled the ball, initiated the offense etc and Bibby was much more of a shooter/scorer than a traditional PG but I didn't view that team as "positionless" either.
The Rockets on the other hand can make more of a claim on that, especially when they start Josh Smith.
I seem to recall that The Big O, Mr. Logo, Clyde & Pearl, the original IT and many more guys who dominated the NBA in their time too. And I'm just barely old enough to remember people talking about how Magic Johnson was going to revolutionize the NBA and soon there'd just be teams of 6'8" guys who could do it all. But it hasn't happened.
As for DeMarcus Cousins, he's a big. To me there's a lot less demarcation (no pun intended) between PF/C as there is between PG/SG and even those lines get blurred all the time. Boogie is a guy who can play in the block or step outside. He's skilled enough to play either role, or change between them. Whether you call him a C or PF (to me) is much more about who the other guy is playing with him and how that player approaches the game.