There are a number of other lock/flow drills from Hapkido schools on YouTube, but these two are fairly good representatives of what you'll see.
So: In the first one, we see someone flowing quite well, moving easily, the other person being driven around by the locks...
...I wonder if it would have looked like that if the person doing the locks had been smaller than the attacker? Or if the attacker had been resisting at all? Go back and look at the motion again---see how the defender created force to use. How much is arm strength and size? How much is body movement?
In the second one, look at how the arm bar is applied---the defender puts their upper-body weight on the arm, and folds over at the waist. That is one way to drop your weight---but what does it do to your balance? What does it mean with regards to the size difference requirements between the attacker and the defender?
and then there was ours...
One of the reasons I continually harp on "drop into a cat stance" during the angle 2 lock isn't because I really need to see you settle into a static stance at the end of the movement. I do, however, need to have you rotate and drop your weight as you perform the lock--otherwise, it is just your arm strength vs your opponent's arm strength. (Remember, the point of stances is so that you can generate power by bodily movement without sacrificing balance and structure.)
We use our center to create force downward during an angle 2, forward then downward (using a front stance) during an arm bar, then rotationally and downward during the angle 1 throw at the end. If you step into a position, stop, then apply the lock/throw--all you are going to do is create a situation where it is your arm strength vs theirs.
That arm bar is a good example for that---if you step, stop, and then try to force the other person downward, they just aren't going to go if they have any strength/stature that is comparable to yours. If you use your upper body to force them down, you'd better be heavier than they are---and your balance had better be really good as you stand there with a resisting opponent with your knees straight and your body folded in half.
Or how about instead, driving their upper body forward with your body weight as you step forward, then roll their shoulder downward as you continue your movment into a low front stance, extending them past their balance point, and downward after they have no more support. Your balance is kept by the good stance, and you are able to move them using your center's movement, instead of your arm strength.
Everything comes from the center. Whether it is for a lock, a throw, punches, or kicks---all power comes from your center's movement. (Granted, it is more obvious to see this when performing a lock.)
When performing a technique, figure out where your center is---then figure out where it needs to go to create the force to apply your technique.