Interesting! I have used mine exactly as you state, usually getting it from the beach to a vehicle, actually. I am not sure that I have worn mine on my back for any more than a quarter mile. The one I have has a comfortable waist belt, and, if the bag is properly and fully packed, it should carry fairly nicely. It weighs on the order of fifty pounds with normal gear.

The number of portages I have done is precisely zero. What is involved? Isn't it mostly strolling along a nice smooth path between two bodies of water?

Something tells me you will disabuse me of that notion.....