We can't reach that conclusion. Their circular step sequence was level 3 both at the GPF and at Four Continents, so we can't say that it would have autmatically been level 4 at the worlds.
They were actually very lucky to receive level 3 at all, because Scott's stumble was at the exit of a twizzle, which therefore shouldn't count and he didn't have another twizzle in the step sequence. Also, their GoE was pretty high from most judges.
In any case, Virtue and Moir are taking their skating to a whole new level IMO. Their knee bend and their flow is improved, they are using their upper body much more than before - which makes everything more difficult - and Scott is going for a level of expression I didn't know he had in him.

All this inevitably takes its toll.
Virtue and Moir hadn't reached their full potential IMO and were not likely to ever do that with their previous coaches who kept them at the same level year after year. How lucky for us fans that they are willing to put themselves through all this hard work. If only they had done it directly after their Olympic gold!