I'd say there was a clear difference in performance over time, not that it was slow, just that it was slower vs competition than in the first year. Also compare Østberg in DS3 and next year same driver with Fiesta. Certainly much of the "difference" can come from the eye of the beholder.
However, Ogier said clearly why he wanted factory support. To keep the development/testing up to stay competitive. Since all teams except M-Sport are factory teams, there was only one recent example to go by for him.