How is propeller thrust vector accurately expressed for airplanes and multirotors?
The term 
$$V_q\cdot{sin}\theta_t$$
is a speed, not a force, so it cannot be an accurate expression of the thrust vector.

Propellers accelerate the air flowing through the propeller disc in the direction of the propeller axis (or perpendicular to the propeller disc), so the force is only parallel to the propeller axis when the airspeed is aligned with the propeller axis. If the airspeed is at an angle to the propeller axis, the thrust vector is tilted towards the airspeed vector. The magnitude of this tilt depends on the speed increase of the propeller stream relative to airspeed.