CY
unprofessional opinion, those Merc engine teams performed poorly in Bahrain so I guess there is something to do with the engine. Apart from the engine, in practice sessions, it seems that McLaren have much less porpoising then Mercedes, hopefully the brake issue wont last too long for them
Yes, in the practice events McLaren was one of the first teams looking good on porpoising, but their solution raised the car rather high above the track. That's normally very bad for a venturi tunnel, lowering the generated downforce significantly and this with those new cars relying heavily on that downforce. McLaren tried to cure that with generating air vortices with the sideskirt supposed to seal of that huge gap from air flowing inwards. Perhaps that didn't work that well.
The picture doesn't look good for the Mercedes engine, but the fastest top speed from Mercedes teams was the Williams. So maybe it's the cars of the other 3 requiring more drag inducing help to sort out their problems and the engine, while I highly doubt it's the best any more, isn't down on power as much as the first race makes believe.