Choosing a Major Essence is on the same level as choosing talents. We decided to make talents and major essence inputs for the optimizer. They change how the game plays/feels substantially and can be highly situational. The optimizer picks gear around those choices that you make.
If you want a general idea of the relative power for talent/major essence choices, you can look at the talent section in our guide pages.
In general, if you are willing to optimizer your gear and play around a particular talent/essence combo, they are all pretty close together. There are a few outliers, but outliers are still within 5-10% at most. Almost all choices of talent and major essence have the potential to perform within 5% of each other.