DL will likely return to last next month cause their increase just started end of last week (although the number of seats aren't much different).

If we put yield in perspective then BR/CI are doing much better than JX/DL. CI can simply adjust cargo flights and put more in passenger belly and fly less passengers as it has quite some operation in SEA. Loadings on J have been reported to be poor on JX/SEA while DL does fill the front cabin (but we don't know if they are non-rev).