This is not the current vision of the game. Devs want telegraphed attacks that you move to avoid no matter your character. Boss fights should be when you tune in and focus where running echoes can be a more mindless affair.
Soem things to consider: were both of these with the same mods? What area and enemy type? Which mods were on each/both, some mods are fine for bosses while others are terrifying and vice versa.
Is this your endurance threshold, or your % endurance. They are 2 related but different stats.
This is being changed next patch with the new monolith changes