And there were enough secondary indications (unstable pitch, dubious airspeed, rapidly unwinding altimeter) that a Captain should have been able to use to diagnose a stall.
More again about Dubois :
The first words he pronounce when entering the flight deck are (Ref CVR)
What are you doing ? So .. as the rest space is only equipped with a buzzer ( employed by Robert) and no phone communication ... before entering in the flight deck Dubois know that's something is wrong .. and he don't ask "what happend ?" but instead the famous
What are you doing ?
Is this question is related with the feeling of not full confidence he can have in his crew ?