Well if a band is educated well enough and work hard enough in their marching they can play complex music and still sound good. Now it takes a little more time to perfect but it's not unattainable.
Take Brazoswood, they march in a minutely bent knee with toes up. Straight back, shoulders back, chin up and tucked. This posture allows better air movement and support. So if the band were to march correctly, no matter what the tempo they could play anything. Infact I personally prefer marching and playing to a "park and bark".