Perhaps one of the reasons why there are so few WCV Wizards (JB once said there were some, but I have yet to see any of them). The risk of being tempted to do Black Magic, the risk of being tainted by it, might be too big a price. Even the darkest of WCV hold onto their mortal souls to some degree. They all know that if the demon did take over completely, it would be worse than what happened to Thomas in TC. They would be nothing more than predatory, feral animals. Not mindless, but not civilized in any way and certainly not themselves.
First the (unverified) WoJ on WCV wizards:
Unverified WoJ from the 2011 Naperville signing:
'Are there White Court vampire wizards?'
Yes, there are. Thomas is middle-of-the-road in power and [ed: think I'm remembering this correctly] the strongest don't get as strong as mortal wizards [/ed], but they can pull off some strong tricks with their Hunger.
We also have this WoJ:
2) Wizards were a hell of a lot more rare in centuries past. Their numbers have increased along with the world population, but back then a given country was lucky if it had produced a single wizard-level talent more than about one generation in three.
Ok, with those 2 quotes out of the way, I'd say we have few WCV wizards because wizards are rare, and with only so many WCV's out there, WCV wizards are even rarer.
And my hypothesis on why WCV wizards likely don't get as powerful as mortal wizards is a kind of, "
my cup is already full" type thing, where the Mortal vessel already has this demonic power that is stretching the amount of power a Mortal vessel can bear, and then if they are a wizard on top of that, they can't fit much wizard power into the room that is left.
Another way of looking at it is when you have a video game that has particular "pure" archetype classes, and hybrids between them, the hybrids do not do the individual tasks as well as a "pure" class because they have to share their net stats with the other abilties they have... I'm not sure I expressed that well. So I will give an example from Old School Everquest.
Warrior class: Best tank in the game. This means that when something attacks him, he doesn't get hurt much, and he can dish out a pretty good mellee can of whoop-ass.
Priest Class: Best healer in the game. Has some spells that hurt undead bad. Has some innefficient spells that can hurt anyone.
Paladin Class: Hybrid between Warrior and Priest. Tied for 2nd best tank in the game. He can handle himself pretty well in a fight, but can't dish out as big a can of whoop-ass, and won't last quite as long, but he's still pretty dang tough. He also can heal, but a priest 20 levels (out of 50 total) lower than he is, could probably do a better job at it. He has spells that can hurt undead too but not quite as powerfuly as the Priest. He also gets a unique, super slow refresh ability that can instantly heal someone to full health.
The WCV wizard is the hybrid. He's not quite as good at wizarding as the fully mortal Wizard, but he can make up for it with some of his WCV tricks.