As I see it, the only argument for OP to stay with AA is that 2MM goal, which might happen naturally (although hot as quickly) from flights where AA and/or partners make the most sense anyway.

Otherwise the choice is whether to jump ship to AS or to DL. Either will apparently work for the SEA work trips, but OP should check corporate travel policy, examine schedules, and sample some fares to see whether one dominates. Beyond this, DL's big advantage is operational reliability, plus generally having fairly customer oriented staff (there are fewer stories of FAs being nasty to customers). AS's advantage would be its partners and FF program, which aren't business reasons for choosing AS over DL, but might matter a lot to the OP.

BTW, some corporate travel policies permit selection of a more expensive carrier if the traveler's status will result in valuable benefits such as free bags or free food, or priority lines and priority IROPs handling, or enable the traveler to work more effectively such as extra room seating or lounge access. You might also be able to make these arguments even if there's no such official policy.