I only watched the first one, but I wouldn't say your problem is arming the ball, so much as it's a broken kinetic chain, caused by a too-stiff motion.
The way the whole shebang is meant to work is that you drive or shift your weight to open your hips, while your shoulders remain closed a moment longer. This creates what pitching coaches refer to as "delayed rotation," caused by the separation of the angles of the hips and the shoulders. See the SECOND freeze frame I captured of Dolgo up above in post #6, and note the difference in angles between the hips and the shoulders. This is the essence of the upper body's purpose in a throwing chain (therefore, the same goes for the serve!). Afterward, the shoulders come around until they're pointing square to the target as well, and the LOOSE, RELAXED ARM is just now getting ready to use that momentum to launch through.
Legs -> hips -> upper body/shoulders -> relaxed arm.
The way you're executing it, your legs are driving your hip just fine, but AT THE SAME MOMENT both your shoulder girdle AND your already pre-locked arm are moving with the hips as a single, locked unit. The result is you get more drive from your legs and hips than someone arming the ball would, but you're getting no boost from anything above that in the chain.
I'm not deeply in love with the Lock & Roll guy, but I think his explanation of the way the chain is supposed to work contrasts with how you're executing it so well that it might be worth a look.
Incidentally, this is the same thing that causes BSSH's "better" forehand (that he posted above) to be ineffective. Note the similarities in the actions of the hips, shoulders, and arm. Your stroke is more effective overall because you've figured out how to add spin to the thing, but the same prescription will improve both of your shots.