Last year Mercedes-Benz knew McLaren were moving to Honda and so will almost certainly have been reluctant to give them the best engines, in case Honda got to look at them. I'd eat my hat if they had the same Mercedes-Benz engines that even Williams or Force India had (and I'd doubt the customer engines are the same as the works engines).
Rubbish.
The engine designs are homologated by the FIA, any variation between the works and customer engines would have to be separately homologated and treated as different models each subject to the different development restrictions.
The Williams FW36 was hitting higher top speeds than the Mercedes W05 at most circuits last year, and while they did have aerodynamics optimised for top speed this would not have been possible if they had a downrated engine. Force India were also not too far off Mercedes, which is fairly impressive for a team not generally regarded as being an engineering-led company like Williams. McLaren were well ahead of both Williams and Force India at the start of the year, but their ongoing development was clearly lacking as even Force India was getting the better of them near the end of the year.
What
is established in this area is that Mercedes had a head start on packaging their car around the engine, and on learning how to get the best out of them. Williams confirmed these areas were a challenge for them early on with the FW36, but we did see them gradually get closer to Mercedes over the year.
This is more the problem. Ever since Project Four (the Formula 2 team operated by Ron Dennis) bought the rights to the McLaren name and shut down the original team, McLaren has operated on a boom-bust cycle of about 10-12 years long.
I would argue that the Honda deal is more a symptom than a cause, because a look at history would show that whenever things go badly for McLaren the inevitable result is that Ron Dennis will go for a new engine supplier. This even applies to 2005, when Mercedes-Benz took it in house, where they had previously just been putting three-point stars on Ilmor engines for their whole time in F1 since 1993 and for a few years in IndyCar.
The Honda deal may have contributed to their lack of improvement during 2014 - they started out on the race podium in Melbourne and ended with a tough battle to hold onto 5th in the constructors' championship - if certain key engineers were being diverted away from the race team to develop the 2015 McLaren-Honda package.
This year they have a new engine supplier, who are struggling with reliability, partly because of the aggressive aerodynamics of the car. The car is apparently quite good (as you'd expect from the guy who's been designing Red Bulls for years), though not as good as a Mercedes-Benz, but the engine is under-developed.
In addition to the power unit being behind on development, it is also understood that McLaren are deliberately running them on very conservative settings optimised for failure prevention rather than performance, which should see them gradually turn it up over the year. If any of the Mercedes teams ran their engines that conservatively they could be plausible packages to put into Le Mans Prototypes to race for over six hours at a time!
This approach only makes sense if they are banking on Honda making some major developments during this year, and consequently holding off on taking the next power units until those developments become available. I think they should forget that and drive fast to learn the most about the power units as possible, even if it means taking a few grid penalties for new power units and having to race through from the back!
The improved aerodynamics designed by Peter Prodromou are a welcome improvement, but they don't solve the handling problems. This is why they made absolutely the right decision to hire Fernando Alonso, because they will desperately need his supreme skill at over-driving an uncooperative car into battles higher up the order against inferior drivers in superior cars.
