When I say that design is sometimes less important than other disciplines, I just mean that (a) an experience can thrive without improved design, and that (b) sometimes "bad" gameplay can help build an amazing experience.
Over the years, one of the most frustrating things about point-and-click adventure games like King's Quest, Space Quest, Grim Fandango, etc., is how seemingly random combinations of inventory and location were required to progress in the game. The designers had clear ideas of the scenario they want to play out, but rarely seemed to care how unclear this action would be for a player. Looking at it strictly through the lens of mechanics, expecting someone to assemble glue + yarn + paper clip and "use" it on the snail in the cave going on little-to-no information might seem like a poor idea, but Monkey Island, with similarly awkward conventions, is an experience many gamers would place in the hall of fame, and still enjoy today. Sure, there's room for mechanical improvements -- information and clues have evolved with the genre -- but if more time was spent on clue cues and interface than on the visual style, characters, and dialogue, would it still have been a classic?
"Bad" as Good
And is it bad design when it benefits the experience? In Monkey Island, failing to guess correctly often led to hilarious commentary from the protagonist, and being stuck meant exploration that led to other awesome character moments. Would the experience be as lauded if the "bad" gameplay never existed? More examples, tomorrow...