Have never tried double coating with TX direct and grangers, it might work ?
DWR does it's main business stopping the outer fabric wetting out (absorbing all the water it can) thus allowing the Gore-tex or whatever other membrane/coating that the jacket uses to make it totally waterproof keep it's breathability. Once this outer fabric becomes soaked you no longer have a breathable jacket causing sweat/condensation on the inside.
In an ideal world the DWR coating would bead the rain on contact and it would simply roll off, thus not needing any membrane at all and giving you a very light and superbly breathable jkt, BUT as soon as pressure pushes moisture against the face fabric it would go straight through. Hence the need for Gore-tex and it's ilk.
You can steel push water through Gore-tex by kneeling in a puddle but your rucsac won't be able to create such pressures. It's all down to hydrostatic head.
Anyway enough of my strange little tangent, DWR is important to your comfort and TX direct is used to top this up (other proofers are available
) keeping your very expensive jkt breathable.......
p.s As an example, if you've tried a really good breathable windproof you'll know you can happily run in it and not get too sweaty, try doing the same in 3 layer goretex and you'll be in the st johns before you know it. Both will use the same DWR coating, very similar outer materials but the windproof will be lacking the membrane/coating of the waterproof