Different people have different likes, thats why theres all different flavors of ice cream. If you dont need a huge 15 oz pack, dont buy one. Your desire to pack small is your way. Others may be different.
Put that 9 oz 3/4 lenght ridgerest inside the pack and it takes up a great deal of room, and is still lighter than most inflatables. Dont stuff the sleeping bag and save the stuffsack wt, and have a pack that conforms to your back better and is self-adjusting for volume of packed gear, and doesnt de-loft the bag potentially.
A loosley packed pack, conforms to your back better and is more comfortable than a tightly packed one. That is one reason some mfgs make large UL packs. Again, different strokes. Find what you like that works for your style.