The frustrating part about playing vs Molten Giants is that it can put you in a situation where doing anything actually puts you farther from winning, instead of closer. Against UTH, you can still safely put 1-2 minions on the board, so you at least have the option of attacking into something. It can be frustrating too, but not in the same way.
Part of the fun of card games is having edge cases to rules of thumb, but I feel that an exception should be the direct win condition of the game. It's okay (and good) to have an opportunity cost associated with directly pursuing the win condition of the game, for example how turn 1 arcane missiles is typically a bad play, but in that case it's not that doing the 3 face damage was itself bad, it's that you'd be better off saving the card to use later.
For example, in Dominion, the win condition is having the most victory points. There's no card that punishes you directly for having victory points. You are punished in various ways for having victory cards in your deck, but that's not the win condition of the game itself, but just the primary way to pursue it, and moreover those punishments are usually subtle (like clogging your hands, or getting hit by Jester).