It probably was a stand alone art. There's a lot you can do with just the few techniques and basic footwork (empty leg etc).. Nowadays the techniques are blended into various systems, but they're there. But as you've seen, there's a LOT of copycat stuff out there that is...wrong.
It's very similar to bare knuckle boxing, with similar footwork and a slightly more sophisticated hand techniques designed for bare knuckle attacks. Reminds me of some Mantis styles, similar concepts.
The modern, categorized forms of Leopard found in CLF are from Hung Ga's 5 animal system (or possibly Li Ga's, but probably Hung Kuen because it is older), which in turn got them from somewhere prior. But we have them today as the result of Wong Kei Ying's training his son in the southern Shaolin animal traditions (at least, that's where they found me).
So the best place to learn them for real is probably a school with a legit southern CMA lineage. Just make sure that lineage is verifiable. I don't know how popular Leopard is in other CMA like northern styles, but we saw that "Lama Fist" looked pretty similar. Ape, Leopard...whatever.