this may be weird but.......ALL CLASSES are good at PvP none better none worst. all about your build and skills
Look at the clerics skills and try again, they could be pretty awesome in a party setting, but in a 1v1, unless they are fighting a mage with no mana that ran out of pots, it's slightly difficult to believe.
However, the idea of a geometrical-shape like way of showing whats good against what, sounds more reasonable.
I am not going to say triangle-like cause there's no possible way you can actually shove 15 classes into a triangle. And saying a thief and a martial artist are in the same boat pvp wise is ridiculous (lest god forsake an unexpected OP PvP class), so dividing in the current format doesn't work in this scenario.
I have to admit one thing though, the good thing that comes out of all this, is that you don't have to make an entirely new character if you aren't using a PvP worthy class.