I thought so too until recently. I played the death out of Witcher 1 and 2 (never read the books), and felt the exact same way you did. The game creators have been far more clever than I ever gave them credit for though: How do you simulate amnesia for the *player* who gets to know anything they can find on the internet anyway? By spending years never letting them experience first-hand parts of their lives from before that point! Yennifer/Ciri as the case-in-point. Until recently I felt no connection there because I'd never experienced any of it.
Several days back I locked myself into the romantic option with Triss (hell, seemed like a good idea at the time!), but now that I've played the game further, finishing the game that way feels so very very wrong that I want to restart it over completely.
Triss and Yen were actually friends, Triss wanted a romantic relationship with you and completely took advantage of your amnesia to get her in. Even during the previous games she outright lied to you on multiple occasions (even about big things) and kept critical information from you. She behaves as if she's always a little unsure where she stands with you, and so tries to romance you more, whereas with Yennifer, she already knows you better than you know yourself, you two basically have an adopted daughter together in Ciri and she's the closest thing you've ever had to a wife. Yen comes across as a (cold as) Ice Queen because she isn't trying to romance you - even though you've/we've never experienced that before in the games, Yennifer and Geralt got way past that years ago. Yennifer becomes fucking awesome in her own way once you get to spend more time knowing her. Hell, Yennifer already died once for you: While she was trying to save you, when you yourself died previous to the events in the first game....then Ciri sweeps both her adopted parents away, setting up the events of the entire Witcher trilogy.
I can't fault how anyone decides to play it, but at this point for me personally, ending the trilogy with anybody but Yen would seem terribly, horribly wrong.
