Morphs V/S Bones for Facial Rigging

Humm not sure what you mean. Almost sounds backwards.

Bones work very well as layers and the same animation sets can be used on 100’s of different characters.

about 16 layers so things like the eyes or mouth opening and closing can be done independent using the same animation takes so clusters works well on video game characters where there is no real need for a high fidelity output. All of the Paragon character models for example are rigged for cluster shaping .

Morphs on the other hand blend based on weight as an additive and only effects vertices that has an offset off of the target

So

Blended morphs gives you a sum total of the additive value blended bones gives you the absolute value