I agree with Roger. Don't worry about it. There are a number of them flying, and most report no issue. The situations I've heard about were either from being very overpowered or high G manuevers at high speed. The instructions from GP are very specific about engine size, weight and speed limitations. I think if these are honored, you will be fine, as others have been. I put in the CF because it adds almost not weight, and gives an extra margin of safety. But I could just as easily have left it out and I wouldn't have worried about it.

The pieces in question that GP provided replaced the original laser cut ply pieces on the fuse side around the stab tube. If you already have it built, it shouldn't be a problem to filet the stab tube with epoxy/milled glass, or even just another piece added on the inside.

I agree the wing construction is a little different, but it's actually just a much larger version of what they use on several other of their models. In GP's tech support FAQ, they specifically mention that the wing tube doesn't extend all the way into the socket in order to reduce stress being in one place. It's done that way on purpose.