You can survive perfectly fine with just in game based items. But if you play Trickster, there's still events. "If your account has been inactive since Sept. 1st you will get free items" for example. Even if you can't afford it, Ntreev STILL releases cash items to players who are currently playing or haven't been online for a while. Unless you just started, there's almost a guarantee than you have at least one cash item/wep/pet. There's that chance that you always sign on at the wrong times too. T_T
I like your explanation of rock paper scissors. Each class can overtake another but in turn they can also be overtaken by another. I'm not too creative with words so I'll use that kind of example in other forums.