Doesn't the idea of how the sword is swung relating to its weight kind of fly out the window, being that Alucard is a Dhampir, and thus has at least some level super strength. Couldn't Alucard probably wield a fricken zweihander one handed?
The balancing would still affect it heavily. Swinging a sword improperly according to how it is balanced can effectively destroy its cutting ability or power.
Western European blades that we associate with knights and myth today tend to spread the weight evenly along the blade with it concentrated slightly above the median of the blade's length to preserve the power in a slashing swing while keeping stabbing as an option.
Far Eastern blades such as Katanas are primarily stabbing weapons with a secondary purpose for rigorously controlled "cuts" as opposed to slashes (as made distinct by the Book of Five Rings by legendary swordsman Miyamoto Musashi) and as such keep much of the weight balance closer to the grip for better control.
The weapons Alucard would have been raised around would have been very Slavic and possibly Turkish depending on whether or not Dracula captured the weapons of his enemies. These were very different from the weapons used by Western Europe and the Far East. They would have had heavy blades curved such that weight is centered towards the tip of the blade with a generous pommel to counterbalance that -- these were unequivocally slashing weapons not meant for stabbing at all. As tested by Deadliest Warrior, the blades used by the army of the historic Vlad Dracula were among the deadliest they'd ever seen when used properly, capable of shearing through flesh and bone alike when swung with reasonable force.
Furthermore, a Zweihander/Bidenhander swung one handed by a supernaturally strong being would still be a giant rapidly moving iron or steel weight around the wielder's body -- being able to heft and swing the weapon does not equate control. It would easily throw Alucard off balance and leave him wide open for a counterattack, and possibly damage his spine regardless of how strong he is; because that strength plus the weight of the weapon and its momentum can make for very dangerous forces acting upon the user's body. Dhampir strength or not, there's no practical reason for it.
Add to that the fact that scholars cannot reach agreement on how a Zweihander would actually even be USED.
Swords are not cudgels -- they have very precise engineering involved and to use them in a manner that is not in accordance with such precision engineering makes the weapon less useful, if not more dangerous to the idiot trying to use it.