Is this a problem? I think this is a perfectly valid strategy and it isn't a guaranteed win even against the computer. It made fighting the monkeys a bit easier, but when I tried it fighting the fire demons and frost sprites, I got it blasted off me. Wasn't too much help against the massive trees either. It can save you in a pinch but it doesn't make for a good strategy except on a few maps.
Nimbus isn't overpowered in my opinion. Most items that use Nimbus will steal the majority of your power tokens. It doesn't prevent my Bash from sending him flying into lava. It can be Purged. It's only one turn. It is no doubt a great card, but only if it's used right. For example, when your opponent decides to drop two Wall Of Fires and a Cone Of Cold on your dwarf mage. Also, since the priest needs line of sight (unless she self casts) it can easily leave the caster vulnerable. Combining that with the fact that it barely leaves room for your Superb Piety, Mail Of The Martyr,Demonic Charm of the 7th Circle, etc. makes it just a good card. *Based on a true story. That happened twice.
Not a problem at all. I agree it has limited strategic uses, I just wanted to give it credit where credit was due(it is a good card) in that I wouldn't have my first win against the Dragon without it. For comparisons sake my second win against the Dragon came from Touch Of Death, a card with even more limited strategic uses in my opinion.