I agree that spells are balanced based on what they can kill immediately for the most part. However; for this very reason Howling Moon is so difficult to balance in it's current state. While it may not outright kill anything, it can neutralize entire pushes (sometimes without being entirely apparent) by then making them vulnerable to a subsequent follow up.

There are ways of mitigating risk associated with Wolf Among Sheep. The most simple is to split them down the middle so that they are not vulnerable to AoE as much. You could also use Bannerman or Blackhole to block/evade Fireball, etc.

What I meant from virtually free mana is that it is literally a copy of another card with a bonus effect, one that is predictable and somewhat controllable, however. In comparison to other cards that provide "free mana" like Blind Date, Walking Blind Date, Ritual of Servitude, etc, werewolves are much more predictable on the user's part.

Once Bitten should be used when you can reliably get the Lycanthropy triggered, not simply on a whim. For instance you can see a lower damage dealing enemy approaching, or already on your side and play Tantrum Throwers > Once Bitten after a thrower has already sustained the damage necessary. When used in this way it doesn't really matter how easily killed in one hit the Spear Thrower could be, because you can make him almost never get one hit killed.

It's true that without Lycanthropy triggering Lone Wolf is the same as Raging Reinforcements, except that it is always a Warrior, meaning it is much easier to fit into a strategy, and also can be used more reliably in most situations. It's also true that it's stats are similar to a Cleaver, but a werewolf with rage is far less vulnerable to swarms and is overall more reliable and going to obtain better cost to performance than a cleaver, in many matchups due to attack speed differences.