Exactly this. There are 3 monster muster cards that are powerful: Vampires, Witches and Arachas (sp?). The witches I can kill with villentretenmerth or scorch easily. The Arachas I just deal with. They aren't THAT powerful anyway. If the opponent plays vampires, I simply spam spies and lose the round. Then there is still the option of using frost and then villentretenmerth. If he has enough cards (or heroes, horn or dandelion) I can scorch them all at once with villentretenmerth.Nah, those two decks can't really counter weather since they have no spy cards besides The Mysterious Elf. Northern Realms and Nilfgaard will just play their weathers after you run out of cards. The muster ability is scorch weak and extremely weak to Villentrentmeth(sp?)/medic/decoy spam.
For clear weather you actually need to pull the card. Even if you have several in your deck, they will only replace other cards you might need. Your opponent doesn't have that problem. What does 3xFrost matter if you can pull your entire deck with spies anyway?
I'm gonna quit now because I really don't wanna go through ALL the options, but the gist of it is that when you play NG or NR you have all the options you could ever dream off. No matter how many monsters the enemy brings to the table with muster, when you are holding a massive deck in your hand, there is always a way to counter it.