I always felt that Gale was weaving a tale of his own in EA (a bit like EA!Wyll was, only slightly more sophisticated). Never fully trusted his words.

There is a chance that
the bit of Weave that he says in EA he was trying to restore to Mystra was actually a bit of Weave that he hoped to absorb into himself to be EQUAL to Mystra, a god of his own, to meet her at her own level.
Not necessarily nepharious, but completely misguided by the standars of gods in all mythologies. As an ironic punishment Mystra said "oh you like Weave so MUCH? Well guess what's the main level of your food pyramid now, eejit."
This would also make Gale the only one in the party who has some experience with that whole "trying to ascend to godhood", which I'm told is a running theme through BG1, BG2, and the Divinity Games.

That doesn't make him a bad person, just the Faerun equivalent of Michael Scott.