A lot of the endurance reduction is from enhancements.
Crushing Impact for example:
Accuracy/Damage,
Damage/Endurance,
Damage/Recharge,
Accuracy/Damage/Recharge,
Accuracy/Damage/Endurance, and
Damage/Endurance/Recharge.
At 50 these total up to 68.9% each for endurance reduction, accuracy and recharge. As well as 101.47% for damage. (I typically will only use 5 of the 6.. I don't get the full value)
In my opinion Energize it too good not to have. A heal is handy. That it has bult-in Endurance Reduction is a bonus.
Hope this is helping. Loved that you did a spreadsheet.