My GHB's are small duffel bags with a shoulder strap. My BOB's are backpacks.
I find the backpacks are more comfortable but the GHB's usage seems better in a duffel format. The duffel holds more immediate stuff that would be needed, especially this time of the year. Most of the contents would be removed and donned before you would set out on foot. E.g. The hat, gloves, boots... would all be removed from the duffel and worn. Water bottles would go in the coat pockets. Once the bag is lightened, it's then lighter and more comfortable to carry with the single shoulder strap.
On a BOB, the contents aren't immediate so I'd want all the straps (2 shoulder + waist) for secure wearing.
Shoulder bag is nice for short walks or if you need to keep accessing stuff in it, but for freedom of movement a backpack is easier for me. It is easier to run with a backpack and it also leaves both hands free. With a shoulder bag, one arm is not really free as certain movements can dislodge the bag or the strap could interfere with some arm movements.
Now, if you go messenger style where the strap goes over the opposite shoulder you don't have to worry about dropping the bag and your movement is back to almost 100% however is it comfortable enough to run with?
Downside, if you need something quickly it'll take longer to get it from your backpack.
I once saw a film of some medic in WW I or WW II , I don't remember. He had a belt with two side pouches ( like two fanny packs on oposite sides) for medical supplies. They were immediately accessible just like two large pockets or like two panniers on a bicycle.
So, I wonder if someone has tried a backpack plus such belt pouches for easy to access stuff. That seems like an optimum setup.
Also BTW, has someone tried a backpack plus a survival/fishing vest ?
Seems like awkward but perhaps someone managed doing it somehow.