You’re right that the issue is the exposed bellows on the arca. I have a foldable 8x10 camera wrapped in the Wanderer camera wrap in a 70L osprey that allows you to open the front in full thanks to the zippers. The bag easily fits the camera, 4 holders, dark cloth, and 3-4 lenses in a tenba byob. An attachable smaller bag is available for additional stuff like water, food, jacket. I attach the tripod to the outside via the side straps.
So in a few second you have access to anything and everything, making the setup pretty quick. The same solution for the arca would make me a bit nervous because of the exposed bellows, since my approach doesn’t offer a rigid protection. Yours does of course. It’s great!