But the air certainly moves fast enough at the moment of taking off, and if the sensors are sensibly sensitive, they should register AoA well before V_1.

EDIT to add:

Hm, Boeing states:

"During rotation, pitch angle is the critical parameter that ensures tail clearance. Once the airplane is airborne and at a sufficient altitude where ground effect and crosswinds do not affect the sensor reading, AOA will provide valid information."

https://www.boeing.com/commercial/aeromagazine/aero_12/attac...