It's 'pay to win' because people would literally be paying real life money to skip large portions of the game and get ahead of those who spent time and effort accomplishing the same thing. Furthermore the current system does an excellent job at keeping old content relevant - which is more than can be said of old content in certain other MMO's. What's next? Allowing people to buy 'optional' NPC's to fight alongside them in a dungeon, thus leading to dungeons to be made even easier to compensate?