Using PR comparisons on either Boston or the New York courses is probably not a good way to justify a fix argument. This isn't Dubai (or London), its not a 26.2 mile track race, there are no pacers and without the tailwind its a tough course. The downhill to the low point at Route 128 is essentially in three fairly steep drops, with the last one (Rodgers' favorite) at the old Grossman's in Newton Lower Falls being perhaps the steepest. Its not like its a gentle grade. Then, after the 4 climbs (including the hospital hill) there is another steep drop down to the BC T stop that has taken the legs of many a top runner. That's nice that 2:07 is jogging for Canova's group but only 7 runners have ever broken 2:07 in the history of the race and 6 of those performances were in 2011 and the 7th was what was perceived at the time as a historic effort by Cheriuyot in 2010. Also in 2011, while the men were crushing the record the women were over a minute slower than Okayo's mark despite 3 ladies pretty much going at it for the last 5-6 miles, indicating its completely plausible that one race can be very fast and the other doesn't have to be. In 2013 Micah Kogo (2:06.56 PB) went out in 64ish with the leaders and was outkicked on Boylston (despite "superior" track speed) for 2nd in 2:10. This year he ran 64ish again and then blew up at the end losing a full minute to Abdi from 40k onward for 2:17. Both Ibrahim Hussein and Cosmas NDeti, both multi-time winners, have DNF'd on the course as defending champions. These things happen.
There are certainly topics worthy of discussion on this thread (not that I believe them necessarily, but this a discussion forum about running after all), including whether you think Chebet deliberately slowed down at the end or not. I was certainly pleasantly surprised watching it live that Meb didn't get caught. Nevertheless, the PB argument isn't very conclusive.
The weirdest Boston Marathon races remain either the Rosie Ruiz marathon or the rainy year (1987) where the majority of the top wheelchair racers crashed into each other in the first mile.