Dre, I completely get what you are saying and agree to a certain extent. Also, let me know if i misunderstood what you were trying to say.
If OP associates the "pump" with lactic acid production then yes it does contribute to muscle growth. Lactic Acid is directly proportional to level of growth hormone produced during exercise. I don't know the mechanism though, so I might be wrong here.
Next, muscles do not know how much weight you are lifting. They communicate in terms of tension and torque. If you can increase tension and torque in the working muscle without increasing the actual weight, the muscle will grow equally as well and minimize the chance of injury from uncontrolled heavy weight and improper movements. For example, there are two ways I can perform a bench press, both with perfect form.
1. I can just focus on trying to move the weight
2. I can focus on contracting my chest throughout the movement
option #1 - I can move a hell of a lot more weight because all I am trying to do is move the weight so my triceps and delts play a bigger role because I am not concentrating on using my chest. (great for strength training not so much hypertrophy) (this is still with perfect form remember)
Option #2 - I focus only on the muscle I am trying to work and consciously think about squeezing and contracting as hard as possible. In this case, my bench press drops a significant amount of weight but I have worked the target muscle much more effectively than option #1 because I have created more tension in the muscle. (great for hypertrophy)
If any of you guys are having problems contracting your chest throughout your movements it's a little difficult for me to explain over text so just watch this:
https://www.youtube.com/watch?v=N9UNwAjVf9M
Now, I am not saying there is a right and wrong way to do things. There is just a more optimal way. If my goal is muscular hypertrophy and I train the way a powerlifter does, of course i will see growth. But if I train in a controlled manner focusing on tension and not worrying about weight I will see much more muscular growth. (don't get me wrong you need enough weight -- you wont grow curling 5lbs in a controlled fashion)
Also, you are spot on with that the function of the bicep is to supinate the wrist and flex the shoulder. And when you say that the full ROM of a bicep curl involves some shoulder flexion/movement, that makes me think you are talking about a little swing of the arms when curling (correct me if im wrong) however, I do not think that's optimal. I think you can stimulate the bicep more if you use less weight and try to do exercises that work the bicep at it's most lengthened position (i.e. incline curls), the mid range of the movement (standing curls), and it's most shortened position (overhead cable curl) rather than trying to exhaust all 3 strength curves in one movement with heavy weight. I might not have made much sense so just watch this:
https://www.youtube.com/watch?v=tqCrNADRl6g