Have you tried a shim?
If you decide the GC isn’t for you , do let me know. I’ve been trying to get my hands on one for months now.I started with Mamba 70, got really comfortable with it. Lately I've been trying other razors, including the Mamba 53 for 5 days straight. I just shaved with the Mamba 70 again, so comparing Mamba and Mamba 70, it's night and day. The Mamba 53 seems better at removing skin than whiskers, and I just couldn't get in the groove with it. The Mamba 70 is smooth and efficient, and I don't get the burn of the 53. Mamba 70 is even better for me right now than the GC 68, although I'm willing to give that more time.
I’ve learned a lotI have all the GCs and Mambas. I assume you had the GC.84? That one is very efficient, but it can bite. The Mamba you have is indeed not super efficient, but I shaved with it this am and I have a solid BBS. Before you give up, I would recommend you try to dial in on the shaving angle for the Mamba because once you get it right, it is a very nice shaver. For that purpose, make sure you have no background noise or music on when you use the Mamba. Let the sound of your whiskers and blade feel direct you to the right shaving angle.
That said, even I will concede that for everyday shaving, both the GC68 and Mamba70 are the easiest tools to use. Both are smooth (with the GC68 the smoothest) and both are efficient enough. Notice how I say "enough". Because neither is in the same efficiency ballpark as the GC84. Both both do what they were designed to do incredibly well. The big difference is the head geometry and the resulting shave angle.
Another razor that is in my rotation is the Fatip Gentile. It has almost zero blade gap BUT it is plenty efficient even as a closed comb. And it WILL bite if your technique is not good. In part because it is the smoothest of all the razors we have discussed so far, which means you'll be cruising over your face with zero effort only to find out later that you paned a few spots right off your face. This razor is fantastic, but requires some patience...both in loading the bade straight and learning the technique. Incidentally, it is the razor that really TAUGHT me good technique. Unlike the GC and Mamba, the Gentile also is more fickle about which blades work well in it where as both the GC and Mamba seem to work with almost any blade for me.
My current weekly rotation is as follows:
2 Days Mamba 70
2 Days GC68
1 Day GC84
1 Day Mamba
1 Day Fatip Gentile
Either way, let me know if you have any questions.