Okay, so. I have this theory, but i don't speak english fluently, please ignore the mistakes that might have, anyways....
I don't think that Chuck is the real light, why?
Light and darkness are supposed to be good and bad, the boys actually believed that, but, he's not good, he's definitely far from that, sooo i think that the real good is Amara.
She was seen as a villain, but, Chuck were the one who said that to the boys, he could be lying (i believed that), i think that because the only thing Amara wanted was a relation with him, she wanted him to apologize to her and the she meet Dean, he showed her the world. He showed her the world that he and Sam believed in and she fall in love with that, you can see that in season 15 when Chuck goes after her, she's doing yoga and she actually liked a person besides Dean, the girl that gives her the massages (and she practically told Chuck to screw himself), she does have good in her heart, and Chuck doesn't, she might control the darkness but she really good and i think that Amara could be really useful in the final battle against Chuck, like she said before, he can't beat her up even in a good day.