Why don't we know the damage multipliers for abilities by now?

It seems like something this sub would have figured out.
We could theoretically build champions with a certain flat attack/defence value and hit the same dummy void target to measure the dmg multiplier. We might not get an absolute value since we don't have a real reference point but we could use someone everyone has like Kael for reference.
We could then have results like: Harvest Jack AOE hits for 1.2 Kael or Warmaiden AOE hits for 0.7 Kael.

I feel this would help us rank champions better.