I came to a similar line of thinking without that mental trauma. A lot of my concepts of vampirism come from Legacy of Kain. Kain's Lieutenants (His "undead sons") were said to take after their "father", with him evolving first and the others following some time after. They didn't start diverging until Raziel "surpassed" Kain by developing wings. That was mostly likely the first divergence, since his fellow "sons" had later developed in different ways. (Immunity to water, spider features, enhanced telekinesis, and so on) which then also manifested in those that they had turned. Plus there was evidence of this again in Blood Omen 2 where some of the bosses were vampires with their own unique abilities. In an unfinished personal concept, I have it so that vampires start with all the weaknesses and progress down the same ability "tree" as their Sires until they hit a certain stage, then they can chose to allocate points to counteract a weakness or enhance a strength or a new ability.