You raise an interesting point here. Is it fine that Creep changes with each rotation?
I would expect faction-defining mechanics like Creep to be stable over time, with selected cards which make them more or less viable, depending on the meta. Point is, we cannot really tell whether Abyssal Crawler or Shadow Nova are too weak or not, because the effect of Creep is going to change over time, which voids the purpose of the present topic.
I think the developers should REALLY consider including a few of the Shimzar cards into Core, which would help defining the identify of Creep and give foundations for the next cards which interact with it.