The strength of the Echo:

As Elidibus stated the strength of the Echo varies based on any given individual's sundered state. Even then, they boast but a fraction of the power that the Ancients once had at their disposal. So anybody on the First who happens to be granted the Echo is still going to be much weaker than someone on the Source who also has the Echo. With the Warrior of Light/Darkness now standing above even that due to being just a bit more rejoined than everybody else on the Source. It also explains why Lahabrea and Emet-Selch could not be defeated through conventional means.