And the memory wipe was caused by not Hydaylen.
The ascians, a terrorist organization, who killed untold millions of lives across the 13 Reflections AND the Source in a misguided attempt to a free their god. Said imprisoned god, was being used as a shield to keep a thick and dense membrane layer around the source to protect it from Meteion's corrupting influence. That when Zodiark was gone, we saw the effects of what happened, that people transformed into Blasphmies and killed their loved ones and neighbors.
After all, why the worlds are filled with suffering, who helped escalate that into cataclymisc levels? Oh right, the ascians.
Oh and to add to the suffering pile, who made the voidsent and sin eaters? Ascians. Ya know things that wantonly kill others, corrupt people into monstrosties, that these things feed off the aether of living people.
Or hey, who taught the various beast tribes a flawed version of creation magic that would result in the primals summoned in this manner to have a compulsion to assimilate aka temper others? A S C I A N S.
Also said primal summonings were augmented with live sacrifice, that if it weren't beast tribe, we would be talking about human sacrifical rites.
Hey, ya know how an ascian can 'possess' someone and take over their body and rob them of free will? That is a variation of the same tempering magic that is instilled into their primals. That said primals without ascian meddling would be far far far far more benevolent than what we actually encountered.
Or hey even if you want to justify it with Elidibus or Emet-Selch or Hythlodaeus, on how you want to have sympathy for them. Its only understandable if you mean the post-mortem versions of them whose souls were cleansed in the astral sea and so they might actually be the proper people they were meant to be rather than what caused the great evils.
Or hey lets go back to Zodiark. Okay lets say the Ascians freed him, the heart was Elidbus and he never got defeated by us. What was their grand plan with Zodiark? Oh you know to sacrifice half the world's population to restore the lives of their people as that is how Zodiark works, sacrifice half of the people to get the desired result. Of more powerful entitys who view the average human, you and me, as flawed and imperfect disgusting things that according to them have no right to exist and are merely mistakes. Of human lives only being viewed as chattel and a thing to be sacrificed later for ascians.
If you think Hydaelyn is still evil after all this, I don't know what to tell you.