I would've made a custom battle system, because I have the know-how and I... well... know everything that needs to be done to create it in a simplistic fashion that would also allow me to distribute it with a small read-me so other projects could make use of what I created and no one has to continually reinvent the wheel but I didn't feel like it because I have a terrible case of laziness. But if I ever decide to make a 2, and I have the plans for one, it'll feature just that.
This was a long-winded post.