I must say that the flaws you mention on the Magadans have not bothered me so far. Except for your points on the inner bags. They are quite stiff and the role tip is more bulky than it could be. Partially because it is so stiff.

But then again, I never take the bags off. I lead the front strap under the seat and the rear strap under the top luggage plate. Combined with some pacsafes that provides enough security for me.
I align the place where the straps are attached to the bags with the top of the luggage rack, that way I don't have to adjust them depending on how full they are.
Combined with a small luggage role on the top plate they provide ample storage for my needs, so never felt the need to strap any additional roll bags on top of the Magadans.
With my SW Motech rack the bags overhang a bit, but not outwards.

No system is perfect though and everyone has different needs and expectations. So if you get the Giantloops, I'm curious to hear what you think of them.