During war, I doubt you will be replenishing your elite army count. Even if you are, you won't be getting as much offense as you would if you spent it on off specs only. Thus as an Undead, you will not be losing elites during the war, unless through ambushes and NS. The conversion of specs to elites is 10-20% at max, and the loss of units on ambushes shouldn't affect the total offensive strength of the Undead.
Halfers have +40% thief effectiveness, so having a higher TPA is quite simple for them. Although, elves have a stronger/cheaper defense. Halfers have the edge due to their stronger thief abilities, which would in turn make them last longer than an elf during war (cheaper thieves also). Forgot about hospitals for Halflings. Since they can't have any, they will lose their armies quickly.