I wasn't comparing teams by average time, which would make no sense. Instead, I used the MIT differential to adjust the Williams times as if they competed in pre-Nationals.
Hypothetically, if Williams was in the pre-Nationals race, with Conn College times +29 seconds, they would have run:
24:12 (1), 24:45 (9), 25:06 (22), 25:26 (36), 25:42 (46) for 104 points
North Central ran (with place adjustments for adding the Williams runners):
24:55 (16), 24:57 (17), 25:01 (20), 25:19 (28), 25:19 (29) for 110 points
Also note that Williams didn't run their #4 (Nikhil DeNatale) at Conn College. I don't disagree that Williams may well be over 200 points at nationals, but other than MIT/Pomona, I don't see anyone else under 200 points.