Originally Posted by bennos

DL is behind UA (which allows regional certs on TCON) and AA (which allows instruments for GLD and PLT, and no instrument needed for EXP). DL is also behind VX (which allows discounted DoD upgrades). In Y, DL EC is behind B6 EMS in terms of legroom, though otherwise EC is a competitive product.

But the real issue here isn't that some low yielding Y traffic may disappear, it's that the incentive for incremental travel to make a higher status level (to increase UG chances) is gone. There is little effective difference between GM and DM to the TCON flyer now. Sure, DL won't miss me when I book a TCON on VX, but now when I'm looking at pricier TPAC fares I'll probably book on NH or JL because I don't need the MQM on DL.

Meanwhile, delta.com lists the TCON flights as mileage upgradeable. As we know, this is currently false advertising since inventory is never opened in advance and mileage UG don't go the gate. But if DL fixed that (and/or made regionals valid on these routes), there'd be more incentive to stick with DL.