The math largely depends on the timeframe.

Yes, the TA will reduce DCI seats for the short term (as 50s are parked early and 90s added). Looking long term, however, going from 255 to 325 large RJs will mean more DCI seats, since the 50s are being pulled down under either scenario.

The company is already thinking two moves ahead in this game, so perhaps you need to consider how many seats will be at DCI when you need to negotiate again?

You can call it the time value of seats.