Muscular development and speed/fluidity are by-products of regular training but you can only improve on them so much as a primary focus. Our primary focus is on sensitivity training which includes awareness of yourself and your opponent in relation to each other. It also includes recognizing the appropriateness of when to defend and when to take the offensive. With training one can improve one's sensitivity much more than one's strength or speed.
There are also fewer training injuries if you train with the proper cooperative spirit rather than a competitive one. Competitive training offers a snapshot of who has more skill at that moment and does have its occasional place, but cooperative training enables both partners to progress and improve more quickly and for a longer period of time with fewer "plateaus" (stagnation).