That's a good idea of putting a GoPro under your car. I race in a foot brake class, and would like to see how my suspension and tires behave while I push the RPM up, preparing to launch.
I think you can tell more from outside the car. Then under the car. Depending on your track & where they allow the crew to stand. Have someone film your back tires. And the back of the car if possible. ( standing at a safe distance of course).The side view will tell you a lot of things. Are you spinning? Is the tire spinning on the wheel? How is the suspension loading up? And how it’s unloading. The rear viewing camera will tell you if the suspension is loading evenly. And if your launching straight. Heres an example for one of my old bracket cars.