I know how to make living dead better while still retaining it's flavor.
Make walking dead status also convert damage you take into healing instead, this way it's easier to get back to 100% without eating all the healers resources but they would still probably need to heal you for some hp. Not only is this flavor approriate (you turn into a zombie kind of status where damage heals you) but it makes the ability much better and gives it unique interaction with some tankbusters. For example during triple titan tankbuster if you survive the first hit, the second would turn you to walking dead and third would heal you up, making it probably the best immunity cd for that fight while still requiring some healing in other fights. Cooldown could be adjusted appropriately if needed.