In the image below, I want to highlight the position of the foot of these two girls. (Click on image to enlarge).
The girl on the right is taller than the girl on the left, as she is in the background, and her stride length is thus longer, naturally. however notice the foot-strike difference. The foot on the right is headed for a clear heel strike first. Contrast that with the foot on the left, where the foot is cambered slightly and mostly flat. You can nearly see the bottom of the foot.
The difference in these foot strikes is important. The flatter foot will be able to bounce back up off the ground sooner than the heel-first foot, which must wait until it has the forefoot on the ground to toe-off with. The foot on the left can also begin to move back under the hips more, providing stability in the right time-frame for the hips. The heel striker on the right will not have the opportunity to bring it back before striking the ground and creating a braking action, in front of the hips, as shown in the next image. (Click to enlarge)
In this image I have combined 2 moments into one image, as their stride lengths don't allow the moment of hip support to coincide perfectly like the foot strike did. What you can now see though is the difference in the position of the hips, relative to the foot upon the weight bearing. Because of this, the girl on the right must overcome her dip, oscillating upward and over the foot. The girl on on the left has less time between landing and coming over her foot, meaning less vertical oscillation, and quicker initiation of the next stride, (faster cadence).
Though one might ask, if the girl on the left is faster and better, why is she losing? This was an informal stride interval, which they started on their own, not a race.
Does this mean the girl on the right is slower? No, not at all. What it means is the girl on the left is more technically sound in her run technique, and more efficient. That could mean more potential for quick improvement, but the heel striker could quickly improve her technique and make bigger and better improvement gains.
Performance and technique don't really have a perfectly direct relationship, until we get to the higher competitive levels of sport. And even then, few athletes have perfect technique, and it is not directly proportional, as differences in other other factors play a big role. But certainly, technique limits the potential of performance and needs to be addressed in all athletes at some point. A simple change in foot strike can dramatically change run performance and especially economy. The more you run, the more important this is, from both a training and a performance perspective.
Notice the girls are both wearing shoes, not barefoot. Barefoot running might help you be more like the girl on the left, but running barefoot is not a shortcut to good run technique, it still requires the knowledge and focus to perform the movements correctly.
Start paying attention to your technique, like foot strike and see what happens with your performance.