i never said the deck is hard to defeat, i can easily get free rounds against king bran decks just by playing my biting frost... the problem is that they're insanely boring to play against, and are about 70% of my matches at any rank.
morkvarg himself might not be a broken card, but when you factor in longships, shieldsmiths, priestesses, and the ability to cycle through the entire deck, then it becomes a problem...
as i said, they biggest change will probably be to king bran, since having him thin 3 chosen cards from the deck is a ridiculous ability. however, i do foresee a change coming to morkvarg in the future... he might not be overpowered by himself, but that's not the only reason to change a card. you also have to factor in the design space for future cards; which morkvarg mechanic might just be a pain in ass when the time comes...
his ability wouldn't have to be reworked in order to change him, all they'd have to do is remove the ability to continuously buff his base strength. the usual "when X, set base strength to Y" (X probably being "the round ends") (they could even increase his original strength to 7-8 if that's the case)