Edit: It was recently made clear to me that the title says "you're are". That's autocorrect for you. Ignore it.
"Gg" means "good game". By that, you're saying that everyone played well and it was a good match.
"Ez" means "easy". By that, you're implying that you stomped them, they did terribly, and it was easy for you to win the match because of how terrible they did.
"You did well" and "you did horribly" aren't the same thing at all.
So when you say "ggez" you're saying:
"Good game, everyone played well! SIKE! Y'all are horrible and I stomped your asses."
So pick one, gg, or ez, because whenever you say "ggez" you're just being a smug bastard.