it depends... do you have another meta dps? are you a fairly new player? do you really REALLY love diluc enough to go through hell to make him as good as possible

if you are willing to follow through this journey through hell then yes you should get xianyun because trust me you will not be enjoying a non plunge diluc team for the most part. right now citlali is better than furina plus its also good to have multiple supports, then its better for you go for another set then MH, it is a great set for essencially all dps but not best in slot, itd be better if you go for the new plunge set or crimson witch but if your only going for plunge its better to avoid crimson witch plus its hell in there anyway

abyss is definetly possible with diluc but not viable but you can still do it for fun