What are the differences between the Echo and having Hydaelyn's Blessing? [Spoilers?]

[Tenkuu]

Im more confuse now, are we talking about our defences and how we fight Ascians? Or are we talking about blade of light ( the only way to kill an ascian ) ?
Why you said that we were helpless to fight Nabriales withouth the blessing, and now you say that we couldnt destroy him withouth Moen's sacrifice ?

As fas as I saw, having the blessing of light doesnt not give us the power to destroy an Ascian ( yet ), we still need sertain elements to do it. On 3.0 was Nidhoog's eye like an example.

I'm not sure which part you're confused by. If Ascians actually fight us with their abilities, we can fight back with only the Echo, as against Nabriales in the Chrysalis, but if they throw a beam of pure darkness at us, our only defense is having the Blessing of Light. If like with Moenbryda and Minfilia we were already on the offensive and had a beam of Light going, we could fight back without the Blessing (ie Light that came from another source than the Blessing), but without it, we were helpless. We could contribute nothing from ourselves without the Blessing. So yes, we would not have been able to kill Nabriales without Moenbryda. Also, Nidhogg can't be used as an example because his power (and his Eye's) is neither Light nor Dark. With the Eye, it was merely an amount of power (aether) that was sufficient to destroy an Ascian soul.