I'm also surprised to see this issue has persisted since EA and people have been begging for content and fixes only to be answered with crumbs - please Larian, listen to your players, you're at an upswing with the attention the game has been receiving and this can very much solidify how people see you as a studio in the future. At least, be more transparent with us about what seems like obvious bias - perhaps there is some reason to it? Or I might be talking out of my ass, maybe someone that's been around since EA knows them better and can clarify.
I've posted this in another thread (about Karlach), so it is repeating myself a bit, but I think this is because they wrote the companions more as protagonists than npcs. My guess this is why characters like Minthara (and Halsin, in his current version) were left in the dust. They are not origin characters.
Example: Gale gets to ascend now, because he was the most popular origin character played as, and ascension to godhood is classic power fantasy fulfillment.