No, I definitely didn't take the damage spread into account, so why would I?
The so-called "average damage," which is the expected value, is pure 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.
Okay, I understand and have calculated it.