My 2 Emerson CQC-7A's don't flex, but they use thicker titanium liners and G-10 scales than the old Benchmade versions.
I had a couple AFCK's (same thickness liners and G-10 scales as yours), and never remember any flex in the handles, but I probably wasn't looking for it.
I wouldn't be concerned.... the lock won't release by simply gripping the knife hard, although twisting the knife into hard material like wood could cause the lock to slip (I've seen this mentioned over the years but have never had it happen to me).