20% win rate? I wish. It's difficult enough as it is to get the 3 wins a week for challenge log...
Your spells *can* crit for high dmg you quoted. However, for consistently getting crits in that range, you need setup. Also, to hope at getting those crits more often, you need party setup. Premades will obviously make a terrific difference, however, for all the GC/servers that do not have that privilege, you have to look at what you can do 1 on 1 (teams that don't attack, so you attack a node with 1 defender; it's 1 on 1. BLM seems to always lose unless I get the first cast without interrupt and got swiftcast up and opponent is from select classes I can solo).