I think a huge factor has to be Vettel. If he was performing like Webber (mechanical failures included) we’d all be saying they had taken a step back this year.
The difference is a highly motivated young German with super quick quali pace and a calm head in race conditions, and also a highly organized team who tend to maximize on strategy (China is debatable).
I’m not actually a big Vettel or redbull fan, just an avid fan of the sport.