Before COVID, AA did have a agent in the connections area at TBIT to help with baggage transfers and ticket issues. There was even an agent at the TBIT ticket counter too. If there wasn't an AA agent, TBIT had general GSA that handled baggage transfers for all the airlines that use TBIT. Not sure if they are still there. Also before COVID, all the oneworld airlines had oneworld Global Support staff that would monitor flights and help passengers with short connection. QF was probably relying on old pre-COVID information.

Regarding the AA planes at TBIT, AA has been sending planes to TBIT since before COVID. Unfortunately it's a long walk but not a new practice.