It's honestly not as bad as you're making it out to be. The dev team are simply following the rules of D&D-styled undead with this one, and it's obvious that a lot of Div's systems pay homage to D&D, so I can't see how this really surprises anyone. It's not going to end mixed party play between the living and undead, it just means that you'll need to use different tactics to keep each of your party members 'alive' which adds a whole new layer of depth to gameplay which I find amusing and interesting.
Undead have a lot of perks that the living don't have. I think it balances things out quite a bit that they're harmed by divine or 'positive-energy' healing magic. In my opinion, if this system poses a barrier for you, and you can't adapt to a game's ruleset, then simply mod it out and play how you want to play. That's what I'm doing with racial stat bonuses if I'm able.
But there are no negative energy spells to use for healing, alas.
