Since you don't rout out all the body but only the two side wings of it, the central, unrouted line of wood will keep up all that stiffness you need for good sustain. Also, sound holes may bring lower the resonance of the body, but that's only a shade of effect. Sound chambers already bring resonance lower, which is highly recommended due to the thick and stiff maple, that would sound very bright and pale without resonance-lowering sound chambers.