Simple Ferrari has an engine that lets them compete. Mercedes engine is still better but it's not enough that a good chassis can compensate for the deficit.
At the same time, Albert Park is a very unique circuit and winning here doesn't guarantee a win in more normal circuits. If Ferrari has similar pace in Shanghai or Bahrain I'll be impressed, but I expect things to swing in Mercedes favor on tilkedromes with more emphasis on engine power, and more towards Ferrari on more aero dependent tracks. I wouldn't be surprised to see Mercedes win the next two races, then Ferrari again in Sochi.
What really worries me is the rate of development of other teams. No way have we reached the limits of these new regulations. Other cars seem plain in comparison what happens when other cars reach a similar level of complexity?