I have bought AA Gift card for $100 in late Jan this year and didn't buy another one since I have read from this forum that AA change the quote categories to gift card and didn't trigger the airline credit anymore.
However, On June 8, 2019, I have bought AA airplane ticket from LAX to LAS and paid by AA gift card for $100 which the remaining amount of $54.30 paid by my Amex Platinum (personal).
It is very interesting that today I am login to my account and find that Amex reimbursement the amount of $54.30 as "Amex airline credit" on June 11, 2019 and when I checked the quote categories of my AA spending of $54.30 it classify as "Passenger Ticket" (it mark that I got 5X membership points for airfair purchase too). I am checking the meter of airline credit and found that I am already use $154.30 for this year.
I am not sure that I got lucky or Amex change their policy that member can use airline credit for direct purchase air ticket.