You did nothing wrong. Agreed. But your choices in the past should of course influence your current ability to win GA. It's no different than guilds who didn't build JTR teams and NS teams. They are at a disadvantage in heroic STR. It's no different than guilds that din't build counters to JKR, DRevan or similar teams. They are at a disadvantage in TW. I see no problem here.
It is completely different than guilds who didn't build JTR teams and NS teams. This is not a disadvantage because of a choice of farming one character over another. Those guilds can eventually build the team they need. In the grand arena, there is nothing that can be done to correct the imbalance created by pairing players based on their GP. No one can reduce a character from level 85 to level 1. No one can change a character's gear level from 8 to 1. Those stats are creating the problem.
Yesterday, my son was paired with a player who has 24 g12 toons, all with 6 dot mods. My son has zero g12 toons. My son levels up all of his characters. His oppenent only leveled up the characters he uses. His oppenent has a JKR team filled with zeta's and god level mods. My son is months away from JTR, nevermind any of the current meta teams. His oppenent has 33% more zeta moves. This happens often. It is completely mismatched and my son cannot play the grand arena this time because of this problem. There is nothing he can do to fix it either. This has nothing to do with "who" players choose to farm or develop, it has everything to do with GP not being a fair way to match players. You are comparing apples to oranges, which is why you don't see a problem.