Good question and after thinking about it some more the method I outlined above is what I'll do
So LW fabric for the inner layer but use the mesh for the down constraint. If you make the mesh 10 to 20% bigger than the Argon it will expand out into the void between shells then use the standard differential cut tables for the outer.
Somewhat cheaper and quicker I think than using baffles
Of course a as we discussed earlier a baffled down bag will be lighter and warmer but the hybrid is probably better for my wants unless a WPB shell was being used and in this case i have the LW Tyvek for that as the separate layer and still less than 800g