I 100% believe the reason they released two vampires so close together is because Mina was a "Break Glass in case of emergency" hero.
Like the character concept designer was sitting around, dreamt up Drifter as this primordial evil cajun vampire, a real cool concept with an unique twist on it right? Then Yoshi or whoever came in and said "Look, we really need a hot slut. Design us up a hot sexy female vampire."
And the guy said "But I already made Drifter as a vampire?"
And they said "Fuck it just put two of them in who cares."
TL;DR, Mina is a design by committee. Keep in mind I'm not saying this is a bad thing, just how it went down.
