I could not complete GW for 2 months and since then I failed only once (when mods had flat health and protection as primary). And yeah I was facing level 70 when I was level 60...
There are several tricks for GW: balance arena and GW. Arena is depth only and GW is breadth mostly. Try to focus on utility toons as well (Boba AB or Dakka Stuns). Preload TM (I did not have that when protection was introduced).
This is a marathon game. Find an elite guild that will coach you and help you fostering your roster. Completing Tank raid even not as a carry will give you the credit you miss in GW.