It sounds as if US is fixated on getting you to SFO from CLT, but there are possible routings on AA, via JFK or MIA, that can get you to SFO the same day--albeit late at night--with even an afternoon departure from STT.

I'd suggest you check these on aa.com, and then call again with a suggested rebooking. Although all airlines are loathe to rebook passengers on a competitor, US and AA are now the same company! The key may be to take CLT out of the problem and focus just on STT-JFO via any routing that works.