Question? we cover all instruments except the altimeter? Could you accurately determine the pitch attitude of the aircraft? You might say if the altimeters climbing it would be a high nose attitude, or if its unwinding it could be a low nose attitude but the point is you could'nt tell me the attittude of the aircraft.
With the attitude indicator you can determine it anytime. I think you might find that when in straight and level flight, you set a pitch attitude and to confirm that this attitude is correct you scan the altimeter.