Completely meaningless. The Slade Evil!Juice is entirely a retcon. At the time Beechen wrote that story, she was meant to be 100% in control of herself. That was intended to be considered accurate characterization. Her being a total douchebag in the recent BATGIRL mini was also intended to be considered accurate characterization, likewise her being a douchebag chatterbox in GOTHAM UNDERGROUND and her organizing the underground in the first place.
Cass is not "not responsible for her actions" under Beechen because she was Slade!Juiced. That's ass-backwards cause-and-effect. The Slade!Juice was invented to account for her bullshit behavior. Just like the Yellow Space Bug was invented to account for Hal's bullshit behavior, or Leslie hiding Steph in Africa was invented to account for the bullshit of War Games.
Bad characterization is bad characterization, period. Bad writing is bad writing. If an author does something stupid and wrong, it's stupid and wrong. Now, the lovely thing about comics is that, sometimes, another author can come along later and invent a whole new story to try to redeem the prior stupidity, and sometimes that's awesome and leads to whole new epic levels of sense and goodness. But that doesn't make the initial stupid any less stupid, or somehow legitimize stupidity that hasn't yet been retconned.