I ran the race too, and watched video of Mo afterwards.
The main limiter on Mo's performance that day, from a viewer's perspective, was the failure of the pace making arrangements. He sensibly decided against following the planned WR pace group led by Geb, and planned to run in a separately paced 2nd group. But then Geb's first group pace was too up and down, and Mo's pacer was a bit confused, and so Mo found himself in no man's land for much of the race, losing the chance of a free ride that so many of the other lead athletes got (and that the Vail/Thompson/Overall group behind him did get). Just after halfway, the race feed shows Mo gesturing in frustration at the pacemaker who is running 40 yards ahead of him.
The weather was pretty darn good, but not "perfect" for marathoning. There was indeed a net head wind. I was running with lots of other athletes (~6:30 pace) all the way, so its effect on me was barely noticeable, though it can be seen in the splits (I was a little faster in the sections of the race where I was running eastwards). But Mo didn't have the same protection that the masses had, or that the lead group had. The temps were good from my perspective (US-based), but the Brits were complaining that it was surprisingly warm for that time of year, and they were right. That was unlikely to faze Mo, though.
Lots of people described Mo's run as a flame-out after such high expectations. And then described the rest of his season as a cop-out, avoiding the hard competition. But in London he went up against the best, and it's really hard to know how he might have fared if he hadn't been running in no man's land for so much of the way.