Soft aluminum and English wheel or sand bag and mallets, even welded/soldered/filed, might still compete with the composites. Also innovative design might make all of them flat wraps, and then hard aluminum and rivets would work. These items are not considered structure, although certainly do not want your cowl to fail and hit the prop.But the cowling, wing tips, root fairings, and other compound surfaces may still be best translated into composites because they are compound curved surfaces.
To me it is builder preference being most important. What do you want to work with?