I offer this question: Would PvP in WoW be more or less active (note that I am specifically not using the words popular or fun) if players used a standardized set of gear?
On one hand, removing gear as a factor would allow players to jump right in at any time, with no grinds to get in their way.
But I suspect this benefit would be outweighed by the costs. For one, gear serves as a scapegoat. How good/bad are you? Who knows! Your gear is a factor, and a convenient excuse, allowing bad players to avoid being discouraged and quitting, since they can get better gear and think that will fix the problem.
WoW on the PvE side is driven heavily by gear. I don't think it's a stretch to say that PvE is the dominant element in WoW. It levels us, it trains us. Note the training part: follow the gear, always, if there is no gear, ignore it. Even if PvP gear was completely useless in PvE, the ability to gain gear attracts players, and keeps them going. The hamster wheel may keep more players on than it keeps off.