Good info by everyone… Now, the different point of view or understanding about the true natures of crow came to a common fact. Hopefully I've got a better conclusion taken from the recent post.

Aircraft has different weight and different wing area. On landing, given with desired alpha and airspeed when an aircraft couldn't establish constant rate of descent for target landing slope, there are two possibilities:

1. Lift produce by the wings is greater than the weight of the plane.
2. Lift produce by the wings is lesser than the weight of the plane.

Considering all lift and drag devices were deployed. To solve for #1 there are 2-possibilities: to add weight or to decrease lift. Solution is to decrease lift.

There are possibilities to decrease lift: reduce flaps, reduce alpha, reduce airspeed, add spoiler and deploy crow. Reduce flaps is good but we need drag, reduce alpha is also good but we have desired angle, reduce airspeed is also good but we need airflow, spoiler is what we need but aircraft has no spoiler so crow is a better option.

Let's also solve for #2, if lift is not enough to support the weight of the plane, there are possible solution. Increase flaps, increase angle of attack, increase airspeed, add high lift device (HLD) or deploy negative of crow. Flaps are already max, AOA is not safe when closer to critical angle, also we have desired angle. Increase airspeed can cause high speed landing, also we have desired airspeed. The only solution left is to add HLD or deploy negative of crow.

Aircraft in between doesn't need anymore crow at all.

Since weight, wing size and airspeed are the factors, I therefore conclude that crow option is based on the wing loading of an aircraft. Some require crow deflection, some are not. Light aircraft require crow deflection. Some require negative of crow or ailerons flaps and these are heavy wing loading jets.