I do see how this could be scrutinized. I think it is always hard in horror films where a hand is taken off to sell the horrible injury. I think you can instantly tell Bruce's hand was just fine underneath the shirt sleeve...particularly, when loading his shotgun. If you think about it: there is about fifteen or so minutes where Bruce spends time against his severed demonic hand...and holds the time well without boredom. Equipping the hand with its own "voice", too, whether or not it is cartoonish, gives it its own personality and Bruce has a foil to play off of. In fact, sad to say, the hand has just as much personality as the cast that soon joins Bruce as he battles the evil dead. My favorite scene, oddly enough, (besides the house "coming alive" to laugh and joy in the evilness that is so pervasive) is Bruce, under the demonic curse, enduring the possession and returning to his human self. Seeing the makeup and contacts turning him into a ghoul, the humanity grappling with the evil in a fight for survival, and the re-emergence of Ash, the hero, is just a cool moment to me. You also start to see the cool of Bruce emerge with the line "groovy" and using "baby" in the dialogue. The chainsaw in one hand and shotgun twirling in the other. All of this builds to the whole persona coming out in full force in Army of Darkness.
Out of the cast, Sarah Berry has the most to do, while the others factor in as fodder. With lots of blood and special effects (and camera work) to build up the evil dead going crazy in the cabin, the characters aren't exactly necessarily on the agenda for taking center stage. This is very much about throwing a lot at you, with these people having the misfortune of winding up in the damned cabin, and Raimi having to disguise the tricks with the budget as it was at the time. I still think this kind of work is preferred over the CGI of Drag Me to Hell.