The logic you're using about The Echo and The Blessing is in hindsight because of what was revealed to us in Shadowbringers and Endwalker. A lot of the things before that and some of the things after it don't really add up. They always used the terms kinda interchangeably, so anyone who'd played for a long time could see this was a massively difficult, but brave thing to try and distinguish at that point in the game.
We know the differences in hindsight, but again we've had people with The Echo face primals such as Arenvald. If Arenvald also had achieved the blessing (all elemental crystals), which protects him from primal influence, would he not also be a "Warrior of Light"? If so, why was he not referred to as such? The entire point was the blessing was what made us a Warrior of Light rather than just merely a "person with The Echo".
The alternative was Zodiark, who had tempered all the other Ancients, would allow the remainder of them to sacrifice themselves to empower him, out of their misguided belief Zodiark would deliver them from despair. Zodiark would become even stronger and there would be nobody left. The exact thing that happened on every other star, which sacrificed themselves in similar ways. Like the ones who sacrificed themselves to Ra-La, the ones who fought a war against eachother and eradicated eachother or the ones who shed their flesh (the Ea) and then thought everything was pointless because they couldn't feel. Like the beast tribes sacrificed their kind endlessly to their primals.
They all had one thing in common: they pursued perfection and the result was their own destruction. The Ancients had that same goal and were headed in the same direction, destroying themselves in pursuit of perfection.
The solution, not being perfect and the benefit of having less aether is being able to interpret dynamis properly as a force to overcome the hardships that come with not being perfect.
In any case, the sundering may still have happened, but we would not have known who Fandaniel was, which we needed to. Hydaelyn may not have known to look out for us, but probably would recognize the spirit as Azem's and connect the dots with all the heroic adventuring.