I'm also guessing that it's not just raw MQD, but CPM too.

Person A spends $75K and flies a lot of good Z fares TPAC for 350K NM for 30CPM
Person B spends $75K and flies a lot of J fares TATL for 140K NM for 53 CPM

(I'm not counting Bonus MQM's as Nautical Miles would be the correct calculation of CPM)

Person B would have a higher customer value score to DL even though they are on a plane less than half as much as Person A.

That's even before you factor in where they originate travel. If person A is in ATL/MSP/DTW and B is in NYC/SEA/LAX they values could get skewed even more while still spending the exact same amount on Delta.