gale never once claims it was without motive. quite the opposite, actually. he had a motive and he tells the player so. he sugarcoats nothing. he's neither lying nor deceiving himself, or the player, about what he did, or why he did it.
he tells us exactly what he wanted:
Gale: We enjoyed each other's company - body, mind and soul. But even so, I desired more.
Gale: You see, no matter how powerful a wizard we mortals can become, we never scratch more than the surface of the Weave.
Gale: Mystra keeps us in check. There are boundaries she doesn't let us cross. Yet every time I was with her, I stood on the precipice, gazing into the wonders that lay beyond.
he also tells us exactly what he tried to do to get it at first:
Gale: I tried to convince her. I pouted, I pleaded, I swore my ambition was only to serve her better. But she only smiled and told me to be contented.
and then, when he realised that this would not work, he thinks her denial means he isn't worthy, and that is when he tells us he changed his plans, wishing to impress her so he could be worthy in her eyes to chance at those wonders beyond:
Gale: As inconceivable as it seems to me now, I shared a bed with a goddess and yet I wasn't satisfied. So I sought to prove myself worthy to her instead.
Gale: We come now to the crux of my folly. Shall I share the story behind it, or would you rather head straight to its sordid finale?
Gale: She restored the Weave, reuniting all its scattered shards. Or so I thought, until in the course of my studies I learned of a book. A Netherese tome in which a piece of the fractured Weave had been sealed beyond her reach.
Gale: 'What if', I thought, 'What if after all this time, I could return this lost part of herself to the goddess?'
i also think it's important to note that he didn't seek power, he sought knowledge - although you could argue that for wizards, both are intrinsically tied.
anyhow, gale realises exactly what his mistake was, even describes it as his "folly" and it's no coincidence that he links his story with karsus's own several times over in the telling.
he knows what he did was wrong. he knows where his mistake was. he acknowledges that he thought he knew better than mystra, and he tells us he is the villain of the tale.
it is only in act iii that he truly begins to crave power (in form of the crown) for power's sake - and it's once more spelled out in the game why - because he feels angry and powerless and is absolutely disillusioned with his own goddess (and any of the other gods), who would have had him kill himself and, in his eyes, refuses to help him, help the group, both with the orb and with the tadpoles, two death sentences hanging over him:
Gale: The gods could aid us if they wished, but instead they cower behind ao. so let us act ourselves.
Player: Are you saying you want to ascend? Claim godhood?
Gale: No, not like that. I don’t want to join them. I want to better them. A god’s powers, paired with a mortal conscience, a mortal heart.
i'm all for a multifaceted gale, yet i feel like we need to look at what he actually says in-game and not conflate separate issues and anecdotes across acts that deserve to be looked at with a bit more nuance than "gale has always been powerhungry!".
