I mean, you don't have to get a champion...
You could always spend it on runes or a rune page, but if you want to get a 6300 champ, I'd suggest Syndra or Ekko, seeing as you play Zed (micromanaging your clone/spheres). However, you can also purchase Diana because she has an interesting kit that helps well in a teamfight, much like the champions you play that are listed (save for Zed, he's somewhat useless in a teamfight unless built correctly)
You actually play some champions that I myself play quite a bit, so I'm somewhat referring to myself for insight.
Also, you don't have to go the traditional route. You can buy a champion that doesn't fit your playstyle and you may find yourself liking the champion. I main Yasuo and play a fair bit of Zed, but I play Vel'Koz, who has a completely different playstyle than Yasuo and Zed, and I still find myself enjoying playing Vel'Koz.
So of course, you don't have to go the traditional route, and say, you can buy Yorick.
Yeah.
Buy Yorick. (you don't have to)