I admire your taking time to study and research information. However, it's not black and white.
There is a time and place in a program for cheating a movement.
Only 30% of A Movement Overload the Muscles
Dr. Gideon Ariel's research has demonstrated what we already know; ONLY 30% of an exercise overload the muscles in an exercise.
That means that 70% of the movement under loads the muscle in a movement.
While the muscles do obtain some benefit from under loaded movements (something better than nothing), a greater training effect occurs when muscles are overloaded.
The overload stimulates growth.
The 90 degree angle of the bicep curl is where the greatest overload occurs.
That because the weight is further away from the body's center of gravity.
The further away the weight is from the center of gravity, the greater the load (torque).
Biceps Curl Overload
Thus, the greatest overload in a biceps curl is at the 90 degree angle.
At the bottom and top of a biceps curl, the muscle is under loaded.
Generating momentum in a cheating curl allows you to overload the biceps more so in the bottom and top part of the curl.
This is one method of insuring the biceps are overload to a greater extent throughout a greater range of the movement.
Arnold's Cheat Curls
Bodybuilding.com - The Real Reasons Arnold's Physique Was Ahead Of Its Time.
"If you've read anything about his biceps training, you know that cheat curls were one of his favorite size builders."
One of the keys to maximize the potential in a movement is to overload the muscle/muscles to a greater extent throughout the full range of the movement.
Effective Supeset Method
1) Preform Strict Curl to failure.
2) With out stopping, preform Cheating Curls to failure.
There are some other training method of overloading the bottom and top end in a bicep movement. Cheating Curls are one of them.