It's not impossible if you just assume C6R5 everything. You literally do the same thing as any other damage calcs. Put your assumed stats in the spread sheet, have a rotation that you're going to be using, use the multipliers to calculate the damage and divide it by the time of your rotation.

The resources are all there, if you really wanted to you could just take someone's C0 Eula damage and update the spread sheets to reflect her C6R5 stats & abilities. It gets a bit tricky to calculate the constellations but with a little understand of the game it's easily do-able.

There used to be a whale team damage calculation in the CN community but it stopped getting updated a long time ago because people don't really care.