Quote Originally Posted by CyrilLucifer View Post
The ability to physically manifest the sword of light using external energy defends this, as does Elidibus telling you straight out that your skill with the Echo was what banished Lahabrea, not Hydaelyn's strength. If Hydaelyn banished Lahabrea, why would Elidibus specifically care about your Echo? There are tons of Echo users out there, we're more useful for our Blessing and direct use of Hydaelyn in that case.

The aether was drained from shielding you from Ultima. What little She had to spare after that was probably used aiding/defending you against the Primals/Extreme Primals, as was Lahabrea's goal and Elidibus mentions in 2.3.

Plus, Hydaelyn has been primary shown as defensive. A shield, rather than a sword. You're the sword, not her.
Even if it was the Echo or not, we will need a ton of aether as a fuel to cast the Sword of Light.