The fact is elves usually doesn't kill before they die. For weakening enemies they're just perfect (or duel that lasts), and helping killing flag carrier. But they don't have immediate damage potential. On offense, their poisons and counter damage won't help them staying alive, but they will damage defensers a lot. On defense, only immobilize is truely usefull, poison will help killing, but not as fast as an orc or an undead can do. My point of view is that they're just annoying, but really good at that , so not so overpowered.
If you want to kill a human as undead, just play shotgun, you taser + shotgun (which is not reducted by armor) a couple of time, then explode and human is dead, it's not that hard. In fact most of the time, when a taser undead hook you, you're dead, it's just a little slower for humans. For that reason, and what you said, I think undeads are allready good, not need to make them stronger in any way (or humans weakers, they allready got weakened in 2.0).
For human mole, I too tried it in several games, before reporting it as potentially broken.