I'm not sure which Barbour I've got - they last for ever, but I keep mine waxed and it has never let a drop of water through. It is one of my favourite jackets, however,...
.... I generally do not use mine with a backpack as it is a very heavy jacket and something more lightweight, flexible and breathable, I find, is more comfortable for an active day with a pack such as hill walking, you get great views of birds of prey from above.
Personally I use mainly a slightly oversize Barbour over really thick wool sweaters when I am in really foul weather and spending a lot of time standing around with no shelter, sitting in ditches/hedgerows or driving open vehicles in blizzards etc.
With respect to the pack causing rubbing damage, I would expect there to be a potential for visible marking, but a lot depends on how well fitting your pack is, and a number of other factors. By now there is no way you could describe my jacket as a fashion statement.
For really active days with a pack I use a Gortex shell from Berghaus with zipped in insulation that I personally find is more comfortable for that use as it is more flexible and lighter in weight. I have never owned a lightweight Barbour.
Realistically, it is a bit like boots, I am unaware of any one design that covers all conditions and terrains, so for safety and comfort you need to purchase what works best for your particular use.
Remember, there were versions of the Barbour jacket used by the UK parachute regiment in the Faulklands war and they certainly used backpacks!
One final safety warning for all low visibility and camo clothing, if you are in difficult terrain, please take something with you that can be seen if you need rescuing along with your whistle, map, gps, fully charged phone/radio and torch.