I think that GG itself is fine, considering the whole meaning is "good game", and is in the very most cases used to show sportsmanship to an opponent. However, when you say "GG eZ", "GG10", "rekt", "eZ skrub", "shrekt", "l2p", "goml noob", etc., I find it fairly obvious that the only intention is to see a negative reaction from your opponent. All of these are basically something you say, just to inform your opponent that you think you are way better than them, that they were an easy fight, that they didn't even get close to winning etc. To say it short; you say it to tell them that they are bad at the game. As previously stated "GG", is however just used to show sportsmanship, while all the variations of combinations you can put together with this word have a whole other meaning. Maybe not by any sorts of definitions, but the way people generally react to this is negative, and can in many cases lead the "victims" into anger, causing them, and not the actual troublemaker to get punished. Personally, I don't really get offended by these terms, but I know a lot of people do, and keep myself away from using them, as I know a lot of people dislike it, and it really does not, by any means make anyone happy anyway (so there really is no point in saying it unless you wanna piss someone off).
"So what can be done?"
I think adding the common combinations into the filter would be a good start. Also, when a word that is caught by the swear filter, I think it not only should block the word out, but also inform the player who said it that the word is not allowed. A lot of people don't understand that the swear filter is there to prevent "illegal words" from being used in the chat, and think that it doesn't really matter if they avoid it every now and then. Now, if someone, after the warning that they are given from the filter, decides to bypass the filter, they simply get the same treatment that they would get for Abuse, no, not for avoiding the swear filter. Why? Because the terms are used to abuse someone. This would be the same thing as "#$%& you, you idiot, you are #$%& at the game!" getting punished as abuse, and not as bypassing the swear filter (if bypassed, of course).
"What if there are a few friends just messing around?"
Hehe... What if there are a few friends messing around and one says "look at my sik hax m8, my aimbot is 2op4u"? That guy gets punished. Simple as that. The same concept should go with other offences, and I am pretty sure it already applies to friends abusing each other for the fun of it. For people reading the chat, it looks like serious abuse, and staff would treat this just as seriously as any other case. So why would new abusive terms be treated differently than the old ones?
"But people will just make new words!"
Then add those to the filter too... This would take devs a maximum of 1 minute of effective work, they just add the words into a text file (at least this is what I have experienced when it comes to filters), and boop, the word is filtered. But people will just create too many terms, way too rapidly for the devs to be able to filter them out, right? No. Words don't just become a common term within the span of a day or two. As of now, pretty much everyone knows the meaning of "GG eZ", but if someone made a new word, not everyone would know it, before it had became a common term used, which could take weeks, if not months. This is about 1 minute of extra work for the devs pr. week to make the community a way more enjoyable place for everyone, with less flaming, and less pointless arguing.