For me AS is the only AA partner that I would be interested in redeeming award tickets on. I am very unlikely to fly on any other OW metal except BA and I refuse to pay BA's exorbitant award fees.

I agree with you about Delta's poor availability of cheap award tickets but the appeal of DL as an additional domestic partner is not because I want to redeem with DL. I just look at DL as another earning opportunity to eventually be redeemed on AS/AA.