Wow, that's... pretty vicious. I was quietly expecting you to win this too - before the wraith appeared anyway, and at least expecting you to survive when it did. It doesn't sound like you've done anything particularly wrong though. The time the wraith spends healing is your best shot at survival but you seemed to miss that, and the fact that the barbarians got involved heavily at the same time is unlucky.
The only thing I can think of is abandoning Resident Evil from the outset, as it sounds like trying to protect it bit you in the backside. That's only with the benefit of hindsight though, not saying I wouldn't have done the same.
There must be ways to mitigate this risk but I'm not completely sure what they are. Moving all warriors in groups would probably help, as you have a turn between a spectre ambush and the subsequent upgrade to wraith plus promotion healing, during which you can counter-attack. At the end of the day though, skeletons and spectres upgrade fast like this specifically when they gain large amounts of experience for winning against the odds, so this is almost always the product of a string of bad luck.
The only thing I can think of is abandoning Resident Evil from the outset, as it sounds like trying to protect it bit you in the backside. That's only with the benefit of hindsight though, not saying I wouldn't have done the same.
There must be ways to mitigate this risk but I'm not completely sure what they are. Moving all warriors in groups would probably help, as you have a turn between a spectre ambush and the subsequent upgrade to wraith plus promotion healing, during which you can counter-attack. At the end of the day though, skeletons and spectres upgrade fast like this specifically when they gain large amounts of experience for winning against the odds, so this is almost always the product of a string of bad luck.