My dear, I am not trying to make you feel bad but if you were not able to train your bird, the fault lies with you and not the bird. All animals are trainable, the trick is to do it the way it's going to work with that particular species and that particular animal. And target training (you don't really need to use the clicker) works for all parrots (even wild-caught).
I don't believe in clipping under any circumstances (and yes, I deal with aggressive birds every single day so I know what you are talking about -only mine are male wild-caught amazons- but I also had a very aggressive 2 year old male GCC I took in from the sister of the original owner and he turned out to be just fine in a matter of a few weeks). I did clip one bird years ago after more than two years of constant aggression and although he could no longer attack me in flight -which was a relief- I regretted it almost immediately precisely because of the change in 'attitude' - he went from an assertive, self-assured bird to one that obviously felt very insecure and vulnerable (he actually hid for days) and I took this as a personal failure on my part.
Please insist on the training. It will take two whole years for him to be the way he was before you clipped him so you have plenty of time to figure out how to make it work with him.
I have had 4 birds in my life and this one is much different than the others. I don't believe the fault is mine at all. I know how to deal with and train parrots. This one is much different and was very aggresive. Also, not all animals are trainable. I am very happy with my decision. He is not depressed at all and has been doing great since he was clipped. He hasn't bitten us one time and has been out of his cage all day every day. Also, birds flight feathers don't take two years to be back to normal, it takes six months. And at that point I will let them grow out and see if he goes back to biting or not. Clipping was a last resort. We have scabs and scars all over us, even our faces and he wouldn't learn so I felt like clipping him was the right thing to do. I was expecting people to be upset with my decision but I am satisfied with my choice.
I'm afraid you will be disappointed if you expect him to regain all his primaries in six months. Parrots have only one full molt a year (pet parrots would, sometimes, have a partial molt around January triggered by the lengthening of the days after the winter solstice) and they always molt half their feathers (too dangerous to molt them all, it would ground them and they would become sitting ducks to predators) so, if you clip this time of the year (when the annual molt is almost done), it would require two years for all his primaries to grow back. Check it out, you'll see I am right.
I've cared for hundreds of birds (I am not counting passerines or columbines, only psittacines) and I can assure you that all parrots are trainable. All of them without exception. Some of them are more difficult than others, that's all. I don't mean to antagonize you (I can tell that you are upset about my posting even though you said you expected negative comments and I am sorry about that) but if I can train a fully flighted, BIG and MEAN 30 year old wild-caught male amazon used as a breeder all his life not to attack me (and I am no Parrot Wizard!), I doubt your one year old GCC cannot. It's a matter of finding the right approach so, please, don't let your upset with my opinion influence you and keep on trying because everybody who knows anything about parrots will tell you that clipping does not make aggression disappear. It just makes the bird so vulnerable that he doesn't dare do anything (very old and sick birds never bite either).
I know what you're saying about the clicker lol it's absolutely impossible for me to use one on mine because she is focused only on attacking the clicker....so I just make the sound with my tongue. The clicker worked great for flight recall training because she was so intent on attacking it I could get her to fly to me from anywhere. 
