why can't one just use AoA in isolation
You can. Naval aviators use it as the prime source on a carrier approach.
In the same category as the old furphy about using a pencil suspended on a bit of string to let the pilot fly in IMC without an AH
You not telling me you can't JT?
A certain test pilot from over the water not far away writes in a book that that was his back up on a round the world venture.