N18 CGC counters

People have covered the basics very well already so I'll just follow up with some other stuff that is a bit weirder but still within the rules. Some people will moan that it's "broken" but like you're up against three CGCs so who cares lol.

Dude you have access to Fearsome. This is incrediby effective against CGCs because their Willpower is so garbage. I'd be giving that to every single fighter I can.

Weird trading post buys
Firstly why aren't you using incindiary charges?

You could also get some shard grenades at the trading post. CGCs have terrible will power, so there's a good chance it'll send them insane. It's Bast 5" as well.

I also had a look at Goliath Terrain... I'm not sure how well this would work but I'm just bringing it up to encourage thinking outside of the box. If there are many scenarios where you are the defender you may want to consider the Relic of the Forge. It has a few bonuses but what I'm interested in is that it allows freindly fighters within 3" to reroll failed ammo checks (great for all those template weapons), and that any enemy fighters ending their turn within 3" of it must take a nerve check or become broken - that's a roughly 42% chance for CGC gangers and juves. Also have a look at the furnace shields. It's not a huge thing, but it does allow you to lay down barricades. It doesn't say anything about placement distance from one another, so you could get creative block off paths with layers of them. They're only 10 creds.

Worth revisiting because you may want to invest in some thing you wouldn't usually.
Shifting from Willpower 8 to Willpower 7 shifts the success rate of your willpower tests from c.a. 40% to c.a. 60%. And of course will is also a cheap skill to level up. So, I think the 10 credits for genestmithing the extra will are well worth it. You can even get it at -10 credits with the Protogoliath option...
Scar tissue might be worth looking into depending on CGC weapon load out. Might reduce the number of one hit charges.

Tactics cards
This totally depends on how your arbitrator is handling them. But Not Done Yet is a pretty good way to get in a last counter attack after being OOA'd. Named and Shamed can get you extra bodies. Tempered in Battle gives you another fighter with Fearsome. I'm sure there's other Goliath ones that will help, but there are some incredibly nasty cards that I have zero qualms using on CGC and Van Saar min/maxers: History of Violence and Dangerous Footing. Unnerving Whispers would be great as well.

You can also use a combination of cards to also give someone in your gang extra actions/movement. Combined with the Overseer skill this means you can usually hurl a brutal CC fighter (stmmed to the gills) at someone very far away. Sure he' still have to pass his willpower check. But if you do it early on in the game then a failure won't put you out of position. I'd try maxing someone's willpower and sending them in with an absolutely insane CC setup.

This will be down to your arbitrator but you can also consider the House Ty or Psi Syndica alliances. These are both sort of ridiculous ideas but they could work. The Psi Syndica alliance makes one of your fighters a Psyker which can be very useful against the CGC. Now I ahad a look and your Stimmer could get his willpower to a respectable 5 via genesmithing...

The Ty alliance give you a psycher (and a fairly meh Null) for free whenever your gang rating is lower than your opponent's. These members also don't get injured or killed when they OOA. The Onmyodo Telepath has some skills that would be great against CGC, but she also has one called Unbreakable Will, which lets everyone within a 9" bubble use her willpower of five. Ah yes. Now you see don't you hehe...

Anyway just some ideas. I think part of the issue is that when regular players encounter OP and mon/maxed gangs, they look for "fair" counters. Leave that for the players who are playing a narrative gang. The min/maxers deserve the most powerful bs you can cook up.
Sounds like you're having success, the trick to CGC is templates, templates and more templates. Also Blaze. But watch out for credit traps like frag grenades.

The true beardy counter to CGC, for anyone else reading this post with the same problem, is Cawdor blaze spam, all the blunderpoles, incendiary grenades and the like you can take screened with a bunch of cheap bonepickers