Just set up a mission in AE with an Energy Melee / Regen elite boss to be defeated. Regen to make the end drain effect more obvious. I did it with an elec/kin corruptor.
The elite boss has the following powers:
Energy Punch (attack with lowest end cost: 7)
EnergyTransfer (attack with highest end cost)
Moment of glory (end cost 3.5)
I opened with Transference (end drain from kinetics which drains all of his end) standing invisible next to the elite boss, he still got his Energy Transfer and his Energy Punch off.
Once all end is drained, Lightning Bolt and Zapp kept him drained.
The whole fight took 1 min 45 seconds. During the whole fight he used Energy Punch (4.8s recharge) 5 times and Energy Transfer (24 sec recharge) 2 times. By far not as often as he could. Recharge times were reduced by Siphon Speed, reduction included in the given timings.
One hit with Energy Transfer would defeat my corrupter, luckily the defense was sufficient. But less attacks also mean a lower probability to be hit at all (5% chance is always there).
Due to its low end cost the elite boss could still use Moment of Glory.
A second time I opened with Siphon Speed and without using Transference. It took some attacks to drain all of his endurance but this happened before he could reach me.
Once a foe is out of endurance, Electrical Blast can reduce the damage output of the foe way more than a recharge debuff.
Enough endurance drain (e.g. done by 2 players constantly attacking with electricity) will keep the foe from using his most powerful attacks.
In Homecoming, the endurance of AVs/Heroes cannot be drained (quick enough) anymore to prevent their most powerful attacks.
Practically the end drain effect is only viable against foes which are not quickly defeated, like elite bosses. But since it takes some time to drain the endurance with attacks either the foe will be defeated by the blaster or vice versa before the end drain effect can be exploited. Ranged enemies are still deadly, of course.
The end drain effect of Electrical Blast is no defense. But together with e.g. the Kinetics pool it can take and keep a foe out of the fight.
An effect of Electrical Blast which is often neglected is the short hold after hitting a foe with an attack. This effect often enables Controllers and Dominators to hold a boss with only one applicication of their hold power.