I don’t think it is rushed. Brandon spends some time on it, but it was never the focus of the book or even their characterizations. In the end Kaladin tells Syl that he wasn’t interested in Shallan romantically, just that she made him feel like Tien did. They’re friends. Looking back at the chasm scene, there was nothing particularly romantic about it? It was a good scene, to be sure, but both readings of it are valid. I loved all of OB’s ending; it felt like an end that made sense considering what we’d been given, and most importantly, it made all the characters involved happy. (Except maybe Syl, lol)
In addition to what’s already been brought up, we didn’t have her POV on the matter. She’s very adept at handling her mental state covertly, to the point where people often don’t notice anything is up at all. Kaladin also wasn’t in the best position - literally - to view her body language. For all we know she was gritting her teeth and sobbing inwardly as she handed Pattern to him.
And welcome to the Shard! Any other SA ships you could squee about?