Triss might be the "underdog" in the books, but in the games? No, not if you count the entire game trilogy.
And I think you're sorely mistaken on the notion that there are more book readers than gamers. I think most people who voted on that poll have played the games, or at least TW3.
The reason why Triss seems so much popular on this forum is because a lot of people came to this forum to voice their dissatisfaction on how Triss was handled in TW3, while most Yen fans are content with how Yen was handled in TW3 so there really isn't much to discuss about her for the average gamer/reader.
Just my 2 cents.
I can understand sone of your arguements but, there are more book readers than gamers when you look at the witcher story as a whole.
The books been out a long time compare to the game (but let's drop this topic for another discussion).
When I say Triss is the underdog it's because she is, not just in the witcher 3, but the entire storyline. Being the underdog means she is a competitor to Yen but she had little chance winning and being with Geralt. She was fighting an uphill battle for his affection. Think about it, in W2 she was Geralt LI but the whole while in the background he's trying to recovery his memories and the players were aware of that. When he does recovery his memories, he goes looking for Yen present.
Developing an RPG is no easy task however, when an organization takes ownership of a character and build her up and develop a fan base like CDPR did with Triss, I find it difficult to understand how they thought it was ok or it would be pleasant to end her story in such a shitty way.
If you develop a game with choices then let it truely be a game about choices. Throughout the game loading screen said every decision has consequences and they may become apparent later. But nothing involving Triss had any meaniful consequences, it affected Geralt and Triss only and no one else.
In Novagrad Triss asked about Yen but there was no way to say, say i broke up with her or I with you lets not talk about Yen, or I'm not thinking about Yen right now or something along those lines. On Skelliga Cerys kept pressing about Yen, but there was no way to say to her there is someone else who Geralt cares about.
At Kaer Mohren Geralt tells his witcher buddies that he and Yen broke up and their reaction is oh. They didn't ask what happen, why or was it because of Triss. I wanted to tell them. I wanted him to have the option of saying I broke up with Yen because I couldn't let Triss go or I want Triss back.
I wanted him to have the option to explain to Ciri too. Triss is like a big sister to Ciri sure but, they are not actually sisters. If Geralt decided he wanted to be with Triss because it made him happy, the choice was was his (my, ours, yours) as a player to make. And I honestly think Ciri will accept it. At first she may question him about his choice to leave Yen, but if his choice makes him happy, Ciri will accept it. Saying that, you do get the chance to pick Yen or Triss but if you pick Triss it's halfed ass because, no one acknowledge the choice not even the game and if you pick Yen nothing happens that already would happen well except the end slide.
I'm sry this shit is really grinding my gear and it's seriously rubbing me the wrong way the more I play.
P.s. happy thoughts, More Triss, More Triss, More Triss.