I think that one race is not enough to judge both a car or a driver. Alonso came second but I still think the Ferrari is quite disappointing since they scrapped (an already bad) last season to focus on this car.

That said, probably Redbull improved much more than others. Not only that, but they were already quite fast in Barcelona in the pre-season testing, were fast since the first race, so they didn't have to revolutionize their cars, just fine tuning them. Other teams are probably focusing too much on that F-duct thing.

Another good argument is that this track is where Schumacher always had good races. Actually, it's the track where he won the most times, 7 out of 17 (including this race). He probably would have performed worse on another track, while perhaps Rosberg would have done a better job.
Further more we are assuming Rosberg would have done another good race here with the old car, which isn't a given fact at all. Also, his final position was quite affected by the initial excursion and the pit-stop inconvenient. Schumacher's race was problem less, so this helps explaining the gap.
Given the car was also quite different, it may be that Rosberg just needs more time to understand it.

The only certain thing is the Redbulls are rockets, and that McLaren needs to check better their front suspensions/tires/brakes as this is at least the second time something like this happens.



EDIT for Matra: SBK was indeed an awesome event this sunday.