Its if the person wants to take the time to learn to make the class they play viable.
People said Ret Pallys BC where crap, proven wrong. People said Warriors are crap in Cata, proven wrong. People say this and that and never really "try" to be good. Their only real skill is complaining.
Will Barbs be viable? Hell yes. They are the strongest atm imo.
Will other classes possibly rule over the barb? My god if you think not...DUMB!
While I think barbs will kick some ass, I can't help but to think back to when i went to the 2011 blizzcon and played a wizard at their pvp area. Ofc balancing has happened since, but at that time I had aout 46 kills / 5 deaths compared to the second top player who had 19 kills. I played against a barb / monk / DH / wizard. They couldn't touch me =D
Staying alive is the number one consideration in PvP, and barbs do have an upper hand in this area. I would say 4 though, not 5, since a faster attack from a wiz or dh could still take them out.
Much of it depends on the format of the PvP arenas too. How much of the environment is available for LoS and duck and cover factors in.
Let say 400k ranged dps vs 100k hp barb - if someone really think that melee class can stand a chance must be naive or just dumb ;). I like even more all those comments about skill and builds - wrong game dude it's all about gear and $$$ at end.