I personally think up to and including Now and Never it is as organic as act 1 Yen one. I really got a sense of 2 people finding their way back together.Agreed, the problem with Triss' romance isn't the writing, it's the disjointed nature of it. Yen's romance is organic, (re)developing over the course of the game where as Triss' romance is reduced to a series of quests which turns it in to a mini-game, a common mistake game development involving romances. What was needed, what is needed is for Triss to have an expanded role in terms of her on-screen time in order to provide time for writing that allows that romance to (re)develop organically as well.
It's just that afterwards yes the Triss paths aren't given the scale of treatment of Yen and comes as stunted jarring moments. If you break up with Yen you get meaty post break up content at Kaer Morhen, if you don't you get even meatier stuff. Yen being closely tied to most of the critical path helps her too later when resources were clearly stretched whereas Triss is very loosely tied.
I think it would have been possible with more effort to make it feel fully developed and by that i don't mean have Triss as some replacement mother figure. Instead include her in UMA Kaer Morhen section dealing with fallout between all 3 in all paths and then expand the lodge stuff later to give her and them some meat to the bone. It's not going to happen now and personally i'm grateful the scrap of meat that was the DLC line addition was given.