Okay, now that the fresh emotions from the race are a bit settled down.
In sports for everyone there are form fluctuations, "highs", "lows" and sort of average. There are different reasons for "highs" and "lows", in F1 largely dependent on how each circuit and conditions suit a car and development cycles - whether something has been freshly introduced on the car or upgrade will take time.
Sometimes some race results are a huge surprise. They are like "outliers" in the form book. Like 2012 wet Malaysia, where Ferrari and Sauber absolutely hit their sweetspot and were 1st and 2nd with McLaren and Red Bull struggling somewhat.
We remember in early 2013 also Ferrari beat Red Bull on merit a few times early in the season by the virtue of better tyre degradation. In the end they were no match to Red Bull over a year. I suspect something similar might be happening this year.
My take is that Malaysia 2015 was also a bit of an outlier and surprise to many. For Mercedes it was a relative "low" in the list of performance averages, while for Ferrari it was a "high". So that's how we got the net result - that "on a good day" in hot conditions somebody might beat Mercedes in a straight fight.
But now I am of the view that the average performance of Ferrari should exceed the one of Williams. While I am still uncertain about, how will Red Bull improve during the season. I am certain they haven't shown all their cards yet. Like everyone expects McLaren to improve (another matter is how much), same applies to RBR.