So I just rewatched 11x23, where Amara was talking about being jealous of Chuck and what he had (with her whole I hated you for needing something else, something that wasn't me), and it sort of reminded me of what you wrote about Sam not quite being ok with DeanCas - that he's all or nothing and how this relates to his relationship with Dean and how Cas could divide that more... (I don't have a question, I just wanted to throw this your way and see what you thought!)
I don’t know if I see a parallel there, to be honest. I think both Chuck and Amara were meant to be tragic figures in some way, but writing gods is a very ambitious thing to do and to me, it didn’t always work out there. Amara’s arc seemed particularly random in some moments, and probably the only thing I disliked about season 11. Like - I don’t know, but to me it was never even clear why Amara should have attached herself to Dean in that way. It was Sam who set her free, after all (and Rowena), and you could argue that Dean had the Mark, but, well - so did Lucifer, and that never came up.
(Also, that timeline was always a bit wonky - so the archangels existed before everything else and Lucifer was able to meet Amara and, what, have tea and crumpets with her before Chuck decided he needed to lock her up so he could create the world? And why would Lucifer give the Mark to Cain, then? And when does this happen, anyway - Lucifer must have been defeated by Michael after that, but - mh.)
What annoyed me the most about all that, to be honest, is that the whole Amara storyline only worked because of the subtext propping it up. We’ve discussed this ad nauseam last year, but just to be clear - she embodied this ‘wrong’ kind of love, whereas who embodied the ‘right’ kind of love? Not Chuck, that’s for sure. And also: Dean couldn’t give himself to her because he was pining for somebody else, and who? And despite being all-powerful and billions of years old, she had to go through Cas to reach Dean and talk to him, because…? No, in a way, this was exactly the same mess as season 10, with Cain and Colette on one side and Dean on the other and Jesus, you can’t have it both ways - you can’t say there’s no weird subtext and then use that weird subtext to keep the narrative going.
To come back to your question, I don’t think that Amara/Chuck/Dean triangle had anything to do with Sam at all, which is revealing in itself, since Sam could have played a major role in that storyline: he’s the one who freed Amara, and the one who’d been praying to God all those years, and Lucifer’s vessel and whatever else, but, as usual, his issues didn’t come up beyond that ‘original sin’ theme that’s been Sam’s thing since the very first season. So, no, the plot was clearly tilted in another direction, which was never fully explored because #no homo.
Also, Amara and Sam are fundamentally different in that Sam would (and has) sacrifice his life for the world, while Amara does not see value in that. Despite her ‘redemption’ arc, if anything, I’d say Amara and Chuck parallel Michael and Lucifer (and therefore, a lot of generations removed, Dean and Sam themselves) but they had even less understanding of humanity, and human feelings, than the archangels had - and that’s saying something.