" a lightweight bow could do great with high kinetic energy." Not really possible. Kinetic energy is a poor predictor of arrow performance/penetration. The kinetic energy formula is based mainly on speed, and lightweight bows are not fast so they will have low kinetic energy unless you shoot a very light arrow out of them.
On the other hand, building an extreme FOC arrow adds weight and will slow it considerably, reducing the kinetic energy, but increasing the penetration potential. The momentum formula, which relies more on arrow weight, is a better predictor of penetration. All other things being equal, a slower, heavier arrow will penetrate better than a faster, lighter arrow.
Regardless, a lower weight bow will not shoot a light or heavy arrow as fast as will a higher weight bow. That's why some folks shoot higher weight bows.