I like the concept of "vampires and liches being the leaders." It evokes nostalgia for Warhammer Fantasy Battles.

I think that's right; we shouldn't equate a mage who has overcome death with a priest in armor and place them in Tier 5. They should either be promoted to heroes or placed in Tier 7.

Liches (and vampires) are best implemented in the sixth installment, where everything is subordinate to religious rituals, and transforming into a lich is a fairly common occurrence, like an initiation into the middle ranks of a cult. At the same time, vampires are the highest rank; there should be fewer of them, but becoming a vampire doesn't require complicated rituals or potions; you just need to buy Namtar's poison on the black market (as Moandor did). This balances their numbers.

In Warhammer, it's stricter because becoming a vampire requires the help of another vampire.