Another thing worth noting is that testing is not the be all and end all... look at Ricciardo.. it was literally all doom and gloom after Feb, come March he ended up doing something rather special in the first, and his home race, of the season!!
Infact I don't remember Ricciardo having a bad season at all in terms of reliablity, the same could not however, as we all know, be said for his (at the time #1) team mate.
Didn't Red Bull have a better car aerodynamically than the Merc infact? Pretty sure the engine was the only difference, but because it was so different to the previous regs it made the difference between RB or Merc winning the Championship.... so unpredictable to say how Mclaren-Honda are going to be performance wise just yet I think... but we'll be able to gauge a good idea between Feb and March I guess, not long now
It's mostly guesswork on who had better aero, it was basically presumed based on the past 4 years but ignored a huge amount of brilliant work done on the Merc, it was brilliant in every way so hard to compare aero without the same engine in there.
As the season went on more and more technical reporter type people seemed to swing from engine only to also believing the Merc aero was brilliant, it's likely it was on par with Red Bull to be honest. The other issue is Red Bull with a worse engine managed to beat other cars with the better engine which could suggest stronger aero but ultimately you have to realise that most of the races they beat Williams... Williams screwed up somehow. Williams to Merc there would be some smaller engine differences(more in how to use it/when to use electrical energy for best effect) and the main differences between them were aero/brakes/suspension/chassis rather than engine itself.
Testing last year we got..
Day 1 last year, Red Bull 3 laps, Caterham 1, TR 15, second day, Red bull 8, Caterham 11, TR none ( second day issues
). Day 3 Red Bull 3, Caterham 10, TR 30. Day 4, Red Bull 7, TR 8, Caterham 54 laps.
At the second test though Red Bull had 14/56/28/15 laps respectively, one good day 3 crap days(for this point where other teams were now doing 100 laps a day). Caterham did 68/65/96/21.
So even though Red Bull had a woeful first test and poor second test, the first test alone Renaults total run laps was 7.5x higher, that his 7.5 times as much data and likely multiple times more bugs found than from Red bull alone. Red Bull had a terrible test but the other teams did SO much better than Renault themselves had no where near as bad a test as Red bull did themselves. This absolutely no doubt helped them for the start of the season. Had the other Renault teams not done the laps they did, the second test would have been less good, the third test less good and Renault would be no where near where they were at the start of the season.
This is Mclaren/Honda's biggest weakness, if they have a great test... they'll be doing WAY less running than any of the other teams, if they have a terrible test, they have no other teams supplementing the data and giving them ideas of how to fix engine problems between tests.