GWFs starts to get hang of PvP once you are at lvl56, where you get your Indominable Strike and Crescendo to lvl3. And by lvl60, it'll be the knowledge of how to handle other classes, when to sprint to avoid skills, etc.. You can lvl through PvP, even if u lose it'll still be good exp as werealchemist said.
At lvl60 as a GWF, I'm doing fairely fine. Key is you gotta know when to use sprint at the moment they use a massive skill, like TR's jumping motion when using the Dazing Strike, GFs using Griffon's Wrath, or any skill that you know is avoidable.