No, I definitely didn't take damage spread into account, and there's no need to.
So-called "average damage," which is the expected value, is purely statistics based on successful attacks. Out of 10,000 attacks, we have approximately 5,000 successful ones and approximately 5,000 unsuccessful ones. We add them together and divide by the number of attacks to find the average. This is essential for calculating the usefulness of a skill, and it's the simplest way to do it.
I'm a little lost in your discussion thread, but I'm ready to join the discussion.
Just rephrase your question or the topic of discussion in simpler terms.
For your term "Expected Value," I suggest replacing it with the more familiar "DPS" for simplification, as it might be easier to understand.