F3G
Please don't Rely on your AI to tell you your AoA! Hold the nose of your aircraft on the horizon - fixed attitude, right? Now close the throttle. Continuing Holding the attitude constant, by your argument means the AoA must be constant...?? It clearly isn't, is it? (unless you have an anti-gravity device fitted, of course)
Put this AI = AoA indicator nonsense out of your mind, "Lest the earth rise up and smite thee....." However, as ol' Lang' said AoA is the difference between where the aircraft is pointed and where it going..... so attitude monitoring is still important