I'm not sure I really get the idea that boons and hexes are more swingy than a lot of other existing cards. Perhaps the randomness is a little more in-your-face obvious. But there's plenty of cards that have something of a "random" effect when you play them:
Playing
Smithy as your first/last action: gives anywhere from +
to +
. Like Harvest but way swingier.
Swindler is obvious, and people have complained about the swingyness before.
Black Market - maybe buy a great card, maybe get no good options.
Golem - Play 2 cards, but you don't know which 2.
Tournament - Maybe a Ruined Village, maybe a Peddler.
Gold - While not swingy when you play it, just as random in terms of when you draw it. Maybe it gets you a Province, maybe you already had more than
without it.
Militia - Maybe your opponent discards 2 Estates and does care, maybe you just turned an amazing turn into a do-nothing turn. More obvious with
Minion.
So yeah, I can see that the "take 1 of 12 random effects" feels more random. Maybe because there's more options, but I think people would complains just as much if it were 2 boons in the pile instead of 12. But aside from the fact that there has always been a huge amount of luck in Dominion, the answer to all of these cards has always been the same... play them often and expect the averages to work out to the way they should. In other words, play enough Werewolves consistently enough, and your opponent will usually be hurt the amount you expect him to be.