the thing you have to look at is that losha comes with fanaticism and that other units do as well.
Chalid Astrakan - 8 strength summoner, can summon the host of erinjin or some such, which can easily wipe out nations
Stygian Guards - 7 strength unit with march andseveral other promotions
Paramanders/Crusaders - 6 strength
Donald Lugh - 9 strength melee spellcaster
Corlindale - 2 strength heavy peace oriented caster
Flagbearer - 5 strength unit with bonuses for other units in stack
Losha is not overly powerful in that list. She has to kill something living for her immortality every time she dies (so i doubt the AI uses her well, and players can easily take her out because of this). And don't forget, she's only 1 unit, someone with scores of stygians is easily gonna wipe out someone with 1 immortal vamp.
Personally I've made the recon line all girls and from hunter onward vamps, because the calabim need earlier vampirism, so that kinda gets you what you wanted heh (tho i moved hunters to tracking like i always do, and all units with vampirism require governors manor=code of laws in addition to tracking)