Yes I do believe him there, @KillerRabbit, because the game never calls his words into question. When Gale learns of the Orb's true nature and is rattled by the revelation, he offers Mystra the same excuse "I only wished to prove myself worthy" and while she calls him out on several things during their conversation, she believes him here and tells him that he already was worthy.
For me the closest thing to how Gale tried to persuade Mystra, which we can experience ourselves, is the boat ride. Here he tries to convince the romanced player to take the Crown for the greater good.* He is clearly deluding himself (which you can point out) but the reason isn't hunger for power but again his desire to prove himself worthy. "Then have me, but have the best version of me." The scene itself and all the interactions that come before it during Act 3 (The circus, the brothel**, the newly repaired conversation about his family name) are set up to show, how ill at ease he is with his human self ("You like so many things about me, that I'd have sooner discarded.") and that magical power for him is a way to escape himself.
In the situation with Mystra, he wanted to prove himself worthy of her gift by presenting a grand romantic gesture, again the magical power is just a substitute while the feeling of being deemed worthy is the real goal. I'd also like to point out that Gale's whole story is very adamant about big, over the top romantic gestures not being necessary or - in the worst case - bringing doom. Which is why self sacrifice as the greatest love does not work in this setting either, it is a bad thing to allow your lover to do something like this.
And I think they did a good job with all of his endings because they are way more nuanced than say Astarion's. Especially the "monster pcs" Avatar-Astarion, Karlach and Flayer-Tav have some overall very lovely variations as far as I can tell. You don't always need a hammer to make a point stick.
* And I love, how they made this his evil ending too.
** Again, I am so glad they changed the player dialogue here so you can now have this conversation without being an utter jerk.
Last edited by Anska; 16/09/24 10:24 AM.