Practicing three-point shots to improve free-throw accuracy contradicts the principle of exercise.

Practicing three point shots to improve free throw accuracy contradicts the SPECIFICITY principle of exercise.
The specificity principle of exercise states that, to become an expert in a particular exercise or skill one should perform that exercise or skill. That is, the things that one do during physical activity should be relevant to one desired outcomes, thus, the training regimen must go from general to specific during training.