Grip geometry and prosthetic solutions analyzed - stump, Krukenberg arm and grip [what we really want / Sci Fi]
To grip well and with ease (as already investigated earlier here), the gripper parameters usually are constrained to reside along that diagram:
With a solid slippery gripper, a complex, heavy mechanism requires at least 5 fingers to stabilize an object in 3D space (if not seven). See left side of the x-axis of that diagram above: the harder the grip surface (metal, wood, plastic), the more fingers are needed and thus the more complex the mechanism will be. Advantages of slippery smooth hard surfaces are the possibility to clean them thoroughly, and their longevity.
With increasing surface friction, less fingers are required. A simple prosthetic hook just has two "fingers" and optimally, both grippers are covered with silicone tubing. Grip is just as good as a heavy complex hard surface hand - but construction is a lot less complex and the weight can be kept a lot lower (or at same weight, the gripper is more sturdy). See right side of that diagram just above.
For grippers at that end of the diagram (far right), it is worthwhile to note that despite gripping beauty, soft deformable high friction surfaces wear down and require replacement. I have gone through tapes or gloves as rapidly as one set a week. Then, you need materials you do not have to order through special channels that cost a fortune but are straight forward.
Now, we are not free in our choices for everyday usage of a prosthetic. I recently learned of a ~ 7kg research prosthesis for robotic research of a multi-articulated prosthetic hand. The researchers could wear it for 20 minutes before their arms would start shaking.