I actually have a feeling that they wanted Living dead to work the way you described but Hp's were unable to enter negative values due to coding and it working in a different way with some kind of stoneskin value that has to be healed through or something along those lines was even more cumbersome so they went the route they did. It would be nice though if they could make it work this way.

For the most part indifferent to the rest really, TBN for 50 blood cost in the way you described dont sit well with me though. Maybe if it was 20 blood or something but half a resource is rough on upkeep and being able to use it when you need/want to.