The passive decay rate has been reduced by half in the next prerelease. This was one golem that didn't get as much practical testing as I would have preferred in the pre-release of the expansion for whatever reason; I think mainly people just tended not to encounter it or use it much. So, I expect this one is going to take some more balancing to get perfect, but I'd started it out on the weaker end of things to make sure it was exploitable strong. Instead we wind up with practically useless, as it turns out. Hopefully 3.012 will have made this better, and we'll see where it goes from there, what else seems needed. It very much needs to cause AIP increases based on vampirism or it really will be overpowered (it can't be healed any other way, after all), but it may need to be made stronger and so that AIP goes up slower from that, etc.
Or -- another thought. Maybe we leave it sort of weak like this, but with no AIP cost to the vampirism after all. Then it's useful, but probably not expoitably so because you can't sustain it for super long. Maybe that's something that is unique among golems to the cursed golem: it's weaker, and you have to attack with it constantly, but there's no AIP associated with it. Or something like that.