I assume he wasn't meant to be level 1 to start with, considering he said it was his exceptional prodigious skill with magic that made Mystra attracted to him, though that doesn't actually make him being a level 1 character much less silly.
I noticed with D:OS2 that Larian has a penchant for introducing level 1 characters with level 20 backstories. It was so bad in D:OS2 that I completely lost interest and stopped playing it after about 3-5 hours. So far, Gale and Karlach are the only ones I've seen in BG3 that have super off-putting and severely out of place for the level of character backstories. I haven't uncovered enough of Lae'Zel or Shadowheart's backstory to tell if they're equally as bad. Wyll seems to be a bit in the wrong direction (but I force myself to make the assumption that you aren't supposed to recruit him until at least level 4, and that makes it almost palatable) ...and Astarion can be excused because he was basically a mindless meat puppet for the last 200 years.
This is one of the main reasons why I want to have the ability to just roll with a party of completely custom made characters. I've been role playing since the 3rd grade (I'm 44 now). Having my NPCs not have any story options at all is much better, to me, than having them have stories that are completely out of place for their level. It doesn't break the experience nearly as much for me to have nothing there as it does for me to be wondering how I'm supposed to believe that they accomplished feats that would require a level 20 character to even attempt while they were still basically level 0.
Yeah it's a weird tendency they have, particularly carrying it over to DnD where "character with extravagant completely inappropriate background" has to be one of the most well talked about beginner mistakes out there. It's not like this is some new territory they're covering lol, people have worked out how to not do this a long time ago.
Gale and Karlach are definitely the worst, like Gale was a full on archmage chosen and Karlach was well known enough in the fucking blood war to be recognized on sight as "demonsbane", meaning she'd have to be elite erinyes tier at least. All of that is just way too much for a level 1 character, both mechanically and plot wise. Like how are you supposed to feel particularly cool when your whole backstory is about how much stronger you used to be, and when you know you'll never hit that point again in game because level cap is relatively low?
Shadowheart and LaeZel are both a little over the top, but it's not a big enough gap for me to really be bothered, most CRPGs have some degree of level compression, and both of those could pretty easily be level 3-4~ in their backstory. Shadowheart isn't the greatest champion of Shar, mightiest warrior in the whole religion, Laezel isn't the grand general of the gith, they're just people who were given a mission, shadowhearts in particular didn't even seem to involve fighting at all.
