Sandbox PvP that's when shit get's serious. Most of you don't even know the adrenaline rush of fighting an enemy and if you lose you lose everything on your character. Depending on what you're carrying you act like it's life or death. Stuff that could have taken hours to get at stake. It's a rush indeed.
Yes but for E-sport the simpler the better like @sprinkles said. Less variables less chance for imbalance.
The only other competitive environment that matches this is E-War (self made term), a game that facilitates digital wars, more or less a good Sandbox MMO. Mortal Online is mainly my reference point. However Sandboxes are the complete opposite their purpose isnt making things balanced but having so many options in front of you that your Alliance/Guild needs to research and it's not only a battle of skilled warriors but skilled minds designing the gear, making new tactics etc... just like real war.