In BG 3, every companion follows what has degenerated into the mainstream path of mystery. Only Lae'zel and Kalach stand out a bit, but only because they are hardly represented in the core game world as representatives of their kind, or in other words: their races are so special that it just doesn't make sense to immerse them in an (additional) mystery.
This is my take on the companion writing as well. They are so fully characterized around their mysteries that they seem to be at odds with the world they are actually a part of.
DOS2 actually suffered from the same problem, but the BG3 companions have the benefit of having a lot of extra writing and interactions to hide that better. That said, the most straightfoward companion in DOS2 (Beast) was also unanimously considered to be the most boring, so this kind of writing is generally what Larian's audience wants.
