This could be a bit like the chicken criticizing the egg or the egg the chicken ...
All are of course important and among the three items you listed I would rank Form, Arrow, and Bow. Form would be on a scale of 10 would be 10. The arrow would be 8, and the bow (sorry bowyers) less than 5.
Have someone perfectly tune a top of the line bow with great arrows and hand it to someone who's form is wanting and impressive won't be among the adjectives describing the adventure.
When teaching someone how to shoot I don't care much at all about the equipment as long as it fits, is safe, and is comfortable. Then we learn to shoot. In fact, I wouldn't even start with a bow when teaching or learning to shoot. A loop of non-elastic string does the trick without distractions.