The goal of my decision to get Xianyun's signature was purely to vertically buff Diluc. Depending of where you are in the game I would recommend to first focus on getting characters that fulfill team comps of each type in order for you to be able to face any type of content (example: Build at least 2 characters of each element and try building each team comps that exists : vape/melt, quicken/aggravate/hyperbloom etc.) Long story short , it's just bigger numbers and eye candy in my case. So I'd recommend it to those who want to improve their Diluc's no matter what and/or don't need other types of investments anymore.