The T5->T5 connection for AA flights becomes a nightmare quickly (most recently, midday yesterday).
There are no kiosks for boarding passes and there are typically 2 agents available who quickly get swamped whenever inbounds have missed connections.
Twice I haven't been able to get my AA boarding pass at my point of departure and both times has resulted in a very long wait in the T5 transit area.
Combined with the usual unavailability of the Fast Track security lanes and its easily a multi-hour labor to get connected.
Maybe its more reliable to just clear immigration and then go to T5 departures now that covid entry requirements are relaxed?