Personally changing it to be something only for the Undead makes sense AND makes the undead origin more special as far as the framing is concerned.
Having people just chose to be "Undead except not really" when there are actual undead around takes away from that.
Yes, that does make sense in terms of context. I don't think you'll get a lot of objections to the idea that Zombie makes sense as an Undead Talent. Larian doesn't seem terribly concerned with "makes sense" or "consistency" though.
However, the issue has little to do with whether the Talent makes sense. The important factor is that in terms of gameplay, it is a terrible idea
for many reasons. The largest one is that 1 of the 6 Companions are Undead. The others are not. They have completely opposed methods of healing. Say goodbye to Healing Ritual and Bless as sources of healing, that will hurt the Undead party member. Regular party members will have to work around mass fields of water and blood turned into poison from Contaminate, and waste memory picking up Poison Bolt to heal the Zombie.
The Zombie Talent is a crippling disadvantage. You lose 90% of the sources of healing in exchange for getting a terrible heals from poison benefit. Except that to heal from poison fields you need to walk around in them wasting all your AP, and then an enemy just blows them up, costing you all the health anyway.
The entire party will have to adapt their playstyle to accompdate the Zombie. That is too much of a burden. It will sap the fun from playing. Fun over realism is always the important thing to remember. Larian should not kill fun for the Undead Race for the sake of a misguided sense of realism.
