I dunno, it still seems like rough economics for US unless there are features of their partner contracts that we don't know about, like tiers or bonuses.
I got about 28k bonus miles to earn my 100k. Even if US sells miles to partners for the price AA does -- 2.2 cents -- that's only about $600 of revenue. It could sell 128k miles directly to customers for $600 all day long. Probably twice that.