Great topic! Having thought about this for years with a back that has recurring (congenital) problems, and Loving the sound of my Alembics SO...
My feeling is, having played many many basses, the mass density of the neckwoods, which is the bulk of the weight, is necessary for the even-ness of the instrument's tone.
My graphite bass is much lighter, and as I recall that was one of the reasons for Alembic's experimenting with the material. The graphite on mine is stable, luckily, and playable. The tone of the graphite bass (Series I long) is considerably different than my wood one (medium Series I fretless); brasher, more aggressive, brighter. I love it. The graphite resonates very evenly, and what sustain ... and it IS much easier to bear on the wearability index...