Dispense with the idea of a camera bag for serious hiking. The only practical solution is to pack your equipment in your hiking backpack.
Get some padded pouches for the lenses, toss other accessories in a mesh bag and put the camera with the lens you use most in the smallest top-load camera bag that will fit. Top-load bags are cheap and not bulky. Some lens pouches are bulky, but there are neoprene pouches that aren't. Look at
http://optechusa.com/ for lens pouches and camera pouches. Some people use a chest harness for the top-load bag so it is always handy, but I find that awkward and I like to be able to see my feet. (Plus the harness looks rather geeky.)
I carry the top-load bag at my left side clipped to my pack with a small 'biner so it stays put. The top-load bag shoulder strap goes across my chest and over my right shoulder. I can quickly unclip the camera bag from my backpack, swing it to the front and get at my camera.
Even for a day hike, I use this method. With a proper hiking pack instead of a camera pack I have room for food, water, extra clothing and some emergency gear. A camera pack is only good around town or within a couple of kms of your car.
Happy hiking.