Undead and mech are a total curse in this game. They take a unit from viable to trash. Lets be honest, no dwarf wants to even play the game since they lose 5k mithril just for thinking about a duel or hitting a potentially strong wall. Mech walkers are still way better than undead, but the perma death trait is SOOOO FUCKKKKING BAD its not even funny. Moving on to undead, they are unquestionably the worst units in the game by a massive margin. Not only do they get totally fucked by Tiadrin and Priestesses, but they also permanently die and dont even remotely come close to being cheap enough to merit being replaced. As the OP pointed out, one stalker is not even close in strength to one swordsman, but they share the same cap space. The only redeeming factor to undead is that you can get 600k of free wall power from farming rank 13 gold undead during speed clear events. This makes a lich wall a total waste of time if you are trying to actually break the wall, but its a free for all for farming shit loads of honor.
The bottom line is that permanent death on mechs and undead is a completely oppressive mechanic with regards to those units. NOBODY uses undead, and dwarves all live in the misery of not playing any pvp unless they risk losing a massive cost in rare RSS. Just remove this stupid ass trait so players can have more diverse armies without worrying about losing loads of resources.