I agree that Esmi is a good source of mundane info, mainly by virtue of her being intelligent and also not a complete lunatic, nor is she a sorcerer. I'd also agree with Sorweel filling this role to a lesser extent.
Akka's good for a lot of the worldbuilding/history/lore of the world "in-universe", but I'm not sure how reliable he is on a day-to-day level.
My knee-jerk reaction is to say that Mimara is indeed meant to be our closest thing to an "anchor" for other POVs, but given just how loopy objectivity/subjectivity can be in Earwa...well, I don't know.
Proyas seems like a reliably honest POV as well, even despite his piety (or, perhaps, because of it).