I think it's exceptionally unlikely for a CX elite to only or even predominantly fly AA primarily because being CX elite on AA gets very little benefits and certainly not the one benefit most elites would like (upgrade).

However, I know of a few AA elites (based in HK) who fly CX 99% of the time (and only fly AA when they have no choice such as on a US domestic flight) and to them being OW emerald on CX isn't that much further down than CX DM.