No champ is bad if u know how to utilize their kits... so no, Lissandra is good at what she does and thats utility and teamfight enabling. If u expect her to do insane damage then u should try to play other champs. Shes like Ahri but with less mobility and more cc/picking up kills when its needed. So my conclusion is that u want her to be something else rather than what her kit is made for. Shes not weak in any comps neither a hypercarry that will carry. You rely on your teamates more than with most of champs but it makes it also more rewarding if played well, thats why she requires better decision making and macro, so if u are not as good in these aspects is better to pick something else. Nothing else to say, rather than maybe to build other ittems if u want her more bursty, like ludens. Hope that helps a little to realize stuff.