@Riot I got a curious question

With the MF/GP rework setting sail and the Fiora going into the PBE (along with planned Darius changes, and Poppy Taric Yorick and I think Urgot reworks) I began to wonder. Which is a harder task, creating new champions from scratch and trying to add something unique to their kits? Or changing around older characters to be more appealing so that more people play them while keeping certain parts that the people who play them already will still love the champ? I now both are difficult tasks but I wonder which is deemed of a higher difficulty.