I think we actually agree on this for the most part. You listed lack of conditioning as number 3 of your reasons for injury.
While this is a very broad topic, posture falls into this. As soon as posture is not optimal, maximal force cannot be generated (reason 5). The body breaks down and a different movement pattern/mechanics are used. This leads to injury. Does this include some of the reasons you listed such as supination of the elbow and knee direction? Absolutely.
I was not refering to S & C work when speaking about weighted balls. The problem is throwing weighted balls is trying to combine S & C and mechanical/timing work. A no-no in my opinion.
I guess we will just have to agree to disagree on the weighted ball topic as they go against core concepts that I believe in.