I was just thinking about how Feyre and Tamlin's relationship ended, and the ways it could have gone differently. Like everyone else (I think), I would have liked to see them talk a bit more. Couples separate all the time, especially after tragic events. They were both depressed and traumatised; it would have been nice to see them talk about this and realise they weren't good for each other at the moment, even if at one point they had been.
I think a lot of people can relate to realising they aren't in the right headspace for a relationship, because they're barely keeping their head above the water. No shame in prioritising mental health. It would have been impactful, too.
The story could have gone the same way from there. They would have broken up, Feyre could still go live with Rhys and Co, and we would have her working through her trauma and eventually falling in love with Rhys.
EXCEPT, it ruins two major plot points.
We wouldn't have had the (ridiculous) Highlord's meeting in ACOWAR, and Tamlin wouldn't have gone to Hybern. This last part is huge because thanks to this, Nesta and Elain end up as Fae.
As of the fourth book (ACOFAS), Feyre and Rhys's story officially ends, I'd say. The rest is just extra, and they're background characters. From this point on, we have Nesta and Elain's stories, which wouldn't have been possible if they weren't Fae. They'd have no reason to be in Prythian, and they wouldn't be immortal.
Nesta is especially vital to the story because of her powers. Also, I haven't read any of the CC books, but from what I gather, she seems pretty plot-relevant there, too.
All this to say, Feyre and Tamlin's relationship wasn't poorly written, like a lot of us were thinking--it was done on purpose. You can't have the rest of the series if you change this bit.