Zero is just fine, for now. If she remains perpetually the same then that'd be a problem. This lack of growth is why Y'shtola is one of the weakest characters. People primarily like Y'shtola because they think she is attractive. Take away her looks and her fans would evaporate, she really hasn't got much else going for her, she's just 'slightly sassy kinda smart lady' and nothing ever changes. If Zero sticks around, I'll want to see more depth from her character but if she is a temporary character, then she is doing fine.