I think the point people are trying to make is that luthiers know far better than any ordinary guitarist how a piece of wood in the rough will work out, in terms of dimensions, shrinkage, moisture rates, stability, potential tone, figure, weight. Because they have experience. The luthier (if they have any real experience) would have a far better idea of this than you, because quite simply, how many guitars have you taken from wood to finished instrument?
To use your session analogy - it's like you being called up to a recording session as a guitarist, then playing all the other instruments because you think you're better than the other musicians, even though you've never picked up a bass or played drums in your life.
Just as an aside, how many guitars with Jarrah, purpleheart, and/or zebrano have you owned or played? I'm curious. Also, 1.25 inch wide sections of Jarrah would equal around a 12 piece body.....you're scrap taking wood from a bank counter and you're worried about compromise on the luthier's part? Joker.