And Beasts heal after killing them and have an advantage versus them (according to the wiki). So why are you using them???
Tech to feudalism, adopt MS and then draft(/build - I can't remember if drafting was closed in MNAI) out a dozen vampires. Feast them up, switch every node to death, and then run over them with high strength E5 spectres.
Is this a specific game (in which case, pictures/save) or many games (in which case, give normal research orders, general map settings and so forth).