I fangirl an unhealthy amount

I feel enlightened!

I think you are right about fantasy stakes. When I think of romance, at least in a Shadowhunter context, I think high stakes, high emotions, massive consequences and, usually, the absence of the luxury of time. Also, usually Magnus walks in on you at some point or another.

I do think of TWP as very romantic books. Part of focusing in so closely on the main four characters is to give those romances space and time. It allows for Kit and Ty to be on a desperate chase across Europe but occasionally have time for squabbling over whether licorice is disgusting (yes, yes it is) or you, know being terrified about the other person's safety (which I find romantic, though not domestic.)

If the question is just whether Kit and Ty ever do anything romantic, I do not know what terrible person would promise a romance between two characters and then never let them do anything romantic. Kit and Ty must reconnect after a bad split, but that in itself is a romantic process. Also, they are quite a bit older than they were in TDA so "I don't know, do I maybe want to kiss this person?" is more like "I desperately do want to kiss this person, but maybe they do not return the feeling."