If anything, I enjoy that a seemingly joke element, like a giant catapult that is meant for flinging dog shit all over New York, can remain a consistent story element through the entire series.
So, when you strip away most of the hijinks, Harley shoots herself across the sky to deal with Captain Strong on his boat, but is shortly followed by the mother of the five sisters who are part of Harley's gang. Crazy mom comes dropping in with an assault rifle and drops Captain Strong (who survives), then turns her ire towards Harley for recruiting her daughters into a gang, dropping the fact that they're underaged. Turns out, the sisters are 14 years old, not 19 as they told Harley, who immediately apologizes, but tells their mother they were out doing good.
Cut to some stuff later, and you know how there was some plot with Sy about someone stealing medical equipment? Yeah, I forgot too, but he caught the woman who was doing so, and that's the transition into the road trip/LA arc, as she was selling stuff to hire someone in order to save her kidnaped daughter. She offers Harley $100,000 to do so, and we've got ourselves the next arc.
Like I said in the intro, I actually really do appreciate the fact that something so dumb such as a scat-a-pult, can remain consistent through the entire series. Other than that, it was entertaining enough, had your standard Harley Quinn jokes, and so on. No big deal losing five members of the gang, as while entertaining, it didn't seem like a long term thing to begin with, so oh well. I'm sure Chad Hardin isn't lamenting the fact that he doesn't have to draw five individual characters on top of everyone else anymore.