OK, let's place ourselves. Proto-D&D grew within the Chainmail miniatures game in the 70s, developing eventually into OD&D by '74. So we want our media environment to be early 70s, late 60s. Let's pick a wolfman/werewolf as our hypothetical enemy player character; what's the state of werewolf stories at this point? The big ones are Werewolf of London from way back in '35 and The Wolf Man in '41. An American Werewolf in London won't be out for a few years yet; by 1981 we're well into AD&D 1st edition, by which time the basic core of Fighting-Man, Magic-User, Cleric, and Thief has already become established. So let's take WoL and TWM as our foundation -- what does "a werewolf" look like in popular conception at this time?
Werewolf of London introduced many of the modern common aspects of "a werewolf". They're anthropomorphic wolfmen, and the condition is treated as a form of disease or a physical condition ("werewolfism" or "lycanthrophobia"); the main character catches it in Tibet from a, like, evil Tibetan guy. It is transmitted through bites, and the transformation is induced involuntarily during the four nights around the full moon and can be induced at least partially by simulated moonlight. The transformation be suppressed or undone using the sap of a very rare exotic plant that grows under moonlight, and the werewolf character attempts to use it to self-medicate. When transformed, werewolves are savage beasts compelled to destroy the things they love and only turn back once they kill something, but retain enough intelligence, for instance, to use clothing to disguise themselves. The werewolf is physically fearsome but does not need special implements to kill beyond physical force or a gun; the transformation reverts on death. The impression generally is of "werewolfism" as a very physical, almost scientific thing.
The Wolf Man pivots back to a more mystical take on things. Werewolves again transmit their condition through bites, transform involuntarily, do not control themselves when transformed, and retain no memory of their rampages. The plant element is absent here, and silver is treated as the only thing that can harm a werewolf; this seems to derive from some German legends on the topic. Werewolves also have seemingly designated victims in their hunts, and know them because they can see pentacles on their hands when in their human forms. Magic can be used to temporarily revert a werewolf to human form, and the transformation again reverts on death. There's again an association with "superstitious" "backward" lands, with the idea here being of werewolf legends having a long history in rural Wales and being associated with Romani people also (no, that's not the term the movie uses). This movie is much more successful than its predecessor and is what largely makes the werewolf into a stock horror monster.
We can see the influence of this in the following years, beginning early. "The Werewolf Howls", published in Weird Tales #36-02 (making it November-December 1941, almost contemporary with The Wolf Man) we see much of the same ideas -- werewolves are associated with superstitious foreign lands (this time rural France), have a humanoid appearance, and are harmed by silver. The transformation is involuntary, traumatic, and occurs with the rising of the full moon. Later entries into werewolf movies, besides various Universal crossover gigs, include The Mad Monster (1942, the werewolf is turned into a berserk wolfman by a special serum made by a scientist furious about being ridiculed, does not control himself, dies in a burning house) and The Undying Monster (also 1942, werewolfism is a product of a hereditary curse, werewolf is killed with regular bullets).
So broadly speaking we can say this about what "werewolves" and "wolfmen" are like by the time a bunch of fantasy nerds are sitting down to play customized wargames in the 70s:
Werewolves can range from purely magical (family curses, hexes) to purely scientific (diseases, simulated moonlight, serums).
Werewolfism is highly physical, and dealt with using physical things (special plants, silver, fire, good old-fashioned violence) more often than with magical means. Werewolves are also physical dangers. They won't enthrall you like a vampire or make evil magic like a witch, they'll mainly tear you to pieces. The exception is that-
Werwolfism is infectious. Get bit by one, you're a werewolf too.
Werewolfism is transformative -- its defining feature is turning from one thing to another.
Werewolves are tough and scary -- if you don't have the right stuff to take one down they'll just keep coming.
Werewolfism is not voluntary -- you can't control if or how you transform and often can't control what you do when transformed.
So then, what does our hypothetical werewolf PC look like -- that is, how do these things filter through the intent of creating an overpowered player avatar? I think that we can at least downplay the involuntary elements -- that simply does not seem like something you would want to include if you're creating a deliberately overpowered PC. I will assume that the transformation element remains. Let's say then that this hypothetical character is a berserker sort of figure, remaining human most times and turning into a berserk whirlwind of claws and teeth during battle; essentially he gets to benefit from being an overpowered monster slash combat encounter during battle and from being a regular human character in other contexts.
And then, what does our hypothetical PC-countering-PC look like? The weaknesses of the werewolf are generally understood as being materials or sometimes rites, and often serve to control or reverse their condition; this plant or that spell reverts their form, that metal cuts through their toughness. Werewolf-fighting heroes tend to be posses of gun-wielding characters, but they're usually outmatched by the wolf -- you need to know their weaknesses to really get them. So perhaps our character-meant-to-counter-another-specific-character is built to deny the werewolf munchkin his ability to turn into or stay a wolf, and perhaps also to use silver knives/arrows/whatever to harm it directly if that fails.
So generalizing that into a standard class, I propose that this potential third player type to be the Herbalist, a class that emphasizes the use of special plants, reagents, substances, and potions, supplemented perhaps with some magical words and gestures, to provide benefits to allies and to hurt or depower enemies -- what we'd call a buffing/debuffing class today, maybe, but also picking up the "sometimes healer" shtick of real-life cleric classes and being able to do precise but situational harm to enemies. In later editions, this maybe gets generalized into an Alchemist class to be a general potions/poisons/acid bombs type of figure.
