The EBD was designed so drivers had to use oversteer so the car (had) to be unstable or loose in the first place which Vettel mastered more than any driver on the grid as it was entirely out of their comfort zone. Vettels speed was because he could preserve his tyres better with this new EBD style of driving and the rest were unable to match him not because his Newey car was miles ahead of anything else.
McLaren actually designed a better EBD than Red Bull in the early stages of 2011 and their rear all season was just as planted as the Red Bull, Vettel was just doing miles better than Lewis and Jenson all year and Webber was nowhere. McLaren were hot blowing the diffuser with fuel rather than cold blowing like Red Bull were with the engine mappings, with pumping out air because the Renault engine had these butterfly flaps for reliability and the Mercedes engine didn't, so Mercedes had to go down a different route. Horner highlighted as well that hot blowing was in fact better than cold blowing during the mid season point until they were able to do it as well.
Also the drivability of these new cars are entirely controlled by the software, same with the brake by wire and that the drivers are more dependent on their engineers getting it right for them. Mercedes as well as having a power advantage also have the advantage of engine mappings and torque control in advance for each drivers because of the vast testing they did.
Let's be honest Mercedes are in a whole different zone with the preparation for their drivers as compared with Red Bull who are still coming at the end of testing with the miles they have done. As also reported in Germany the Renault engine mapping is vastly more aggressive in response as they're trying to keep up with Mercedes which can heavily punish any driver if the software doesn't suit the driver. The closer the Renault power unit gets to the Mercedes, the less aggressive the response and more refined like the Mercedes it will become.