Not a big data point, but here goes ...
I've been commuting MSP-BUF on NW for a few months. My routing has been MSP-BUF or MSP-DTW-BUF on the way out, and BUF-MSP or BUF-DTW-MSP on the way back.
The MSP-DTW legs, the BUF-DTW and BUF-MSP trips (Thurs or Friday to BUF, returning on Monday) are almost always 100% full. I'm sure Yield Management is not that perfect, so there must be a few bumps occuring there.