It's true. As long as it is becomes more common knowledge that the system for corralling the "estimated finish" (or non-POT corrals) is a simple drop-down = Corral F, G, or H, then you're likely to see a bulge in that particular corral. Even if they changed the non-estimated finish to say 2:46-2:47, 2:48-3:00, 3:01-3:15, and 3:16-3:30 having a total of 4 corrals instead of 3, I'd bet you'd still see a significant number of runners of the field in the 2:46-2:47 corral whether that's reality or runners choosing the fastest possible corral without required POT.
That was pretty much the case for the 2017 Marathon Weekend:
Corrals J, K, and L were all runners who stated their estimated finish was exactly 5:30 (back then you typed in an estimated time and roughly 6000 runners said their estimated finish was the fastest possible non-POT submittable time). Presumably they randomly distributed those runners over 3 corrals. But there were still 6000 runners that chose a very narrow estimated finish and they evenly distributed ~2000 of those runners into three random corrals (J, K, and L).
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So runDisney for better or worse has since decided to move to a single much larger back corrals with mini-waves. Presumably less questions about why someone is in J vs L and less volunteers (maybe?) needed on race day because there are less corrals to actually manage. Certainly doesn't make it the right or wrong choice, but merely what they seem to be gravitating towards at the moment.
The other possible fix is to move the POT requirement from 2:45 and 5:30 to something slower like 3:15 and 6:30. But doing that has potential negative side effects as well.
All that being said, I try to pay attention more to the number of runners ahead of a certain corral rather than what the letter of the corral may be. Because the # of runners dictates how many other people are around you at the beginning and during the race.
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In the 2018 marathon, 54.6% of the bibs were in the non-POT corrals. In the 2018 HM, 61.5% of the bibs were in the non-POT corrals.