Gamma is 90 degrees (vertical) if you only have one weight -- the unconstrained cable will align with the weight.

And if there is no vertical center cable, the weights will fall until gamma is 90 and the weight is held by the lower cables If you then added a vertical cable and started pulling, gamma would increase until it got to 45 degrees and not get any greater becasuse the horizontal components of the cable tension is only in balance at 45. Okay, not 45, but a constant angle depending on how far apart the weights are.

Our disagreement about your example seems to be whether the lower cable tensions are added as vector sums or arithmetic sums at the vertical cable. You say vector in first figure, arithmetic in second, though I don't see the difference. I say arithmetic in both. Even if you were correct, the angle of the cable at the cantilever arm directly effects the mechanical advantage of the brake, which you do not seem to be taking into account in your model.