The whole engine thing is pretty intriguing. Mercedes looked a fair bit quicker than Ferrari along most of the straights and every time I looked were continuously beating them in the speed-traps at the top of Raidillon, meaning Ferrari's advantage out of the corners had already diminished.
It's something Horner has mentioned a few times - it's not the outright power of the Mercedes that's impressive, it's the mid-range power - they scrub off less speed going through a quick corner than their competitors. You could see that at both Raidillon (speed trap) and Blancimont (onboard speeds). Pouhen likely would have been the same.
Vettel managed to slip-stream Hamilton through Raidillon and got a great run, but once past him Hamilton was equal and threatening to come back, so either Ferrari had more drag/downforce or the Ferrari doesn't have the top end of the Mercedes.
How that transpires at Monza will be interesting. Ferrari's strength out of the corner is impressive of course, and that will help to a degree all along the rest of the straight, but they can't use that for long onto every long straight at Monza - Mercedes could have an advantage from 1/3 of the way along each straight. If the Spa analysis is correct then I think Monza will be much closer than many people are expecting.
Put simply I think Mercedes are just grumpy that they don't have a massive engine advantage anymore. They've had it easy for four years and now with Ferrari power (and potentially Honda in the Red Bull next year) they've got their hands full and don't like it. From the outside given all their grumpy noises it appears it's not a challenge they are relishing. They can still win this year as there's plenty of tracks that should suit them more than Ferrari (if Mercedes are still better mid-corner then Sochi, Suzuka, Austin and maybe Mexico will all play into their hands and should let them keep their championship lead).
Ferrari are strong, but I'm not sure there are enough Ferrari tracks left for them to overhaul Mercedes, providing there aren't any reliability issues (and look at how last year finished!). There are unknowns such as Singapore, where Red Bull could win or easily have two cars between any of the top four, making for quite a big swing.
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