I can only agree.I had some good discussions about this topic and I can understand both sides because I played the Witcher Games before I started reading the books and while playing the Games I liked Triss more because she was kind and of course beautiful.
But then after playing the Games I fell in love with the Witcher World and had to read the books.
After finishing The last Wish I fell in love with Yennefer and her Relationship with Geralt and just think they are perfect for each other, including her relationship with Ciri who is like a daughter for her
I did it the other way around. I guess we're also opposites in that way. I started reading the books because I wanted to get into the games. I figured it would be better to first read the books and then play the games as it would make me appreciate the games more. And in a way it did, but not in the way I expected (I'll get back to this later).
And unlike for you The Last Wish (I assume you're talking about the short story here, not the book that short story appears in. I gets find of confusing with that title...) is what started my dislike of Yennefer. I will also respectfully disagree with you about them being perfect for each other. And here it gets interesting as this sort of plays into what I mentioned before about interpreting stuff as a reader. Most of the short stories are obviously based on well known fairy tales: Snow White, Beauty and the Beast and The Little Mermaid being the most obvious of them. People agree on that. But in my opinion (and some people agree with me on this, others don't) Last Wish also does this. Djinn's obivously exist outside of the Witcher universe. And they are often evil beings that grand wishes. Expect the djinn will try to turn the wish back on its master. This was to teach people a sort of 'be careful what you wish for' moral. I fully believe the Last Wish took this and made Yen-Geralt whole relationship the 'be careful what you wish for thing. That's the whole point of their relationship: Evil djinn makes it so they are not happy with each other, but also can't live without each other.
This changes later though as their relationship gets a bit better later on. I actually expect that Yennefer was originally not written as a permanent love interest for Geralt, that is just my speculation. Either way, just about every charcter in the witcher universe (including Eskel and Dandelion for example) agree that the Yen-Geralt relationship is a toxic one. It was never supposed to be a fairy tale perfect relationship. Some people like that it's more real. They have problems. They have a tons of shit to work through to be together. Their relationship isn't always pretty to the point it is abusive.
One of my favorite quotes from the Witcher 3 is actually about the whole Triss-Yen thing. When you are in the Triss romance in Wild Hunt, Ciri will ask you why you chose her over Yennefer. Geralt will answer 'Hmm. With Yen it was fight after fight, lots of arguments, drama... Not saying it was bad, but... Got to be exhausting. With Triss, it's not. I finally feel... harmony. A calm. Feel like things are finally the way they are supposed to be.' It almost feels like it's sort of a realist vs idealist battle. And of course it matters which you like more: Adventure and drama or calm and comfortable.
Also... Ciri always tends to pop up in these kind of friendly debates, doesn't she? I understand why, but I also feel like she is being used a bit too much as a shield for Yennefer. Some people bring the Ciri argument better than others, but I've also seen some people use her as an answer to all the shit Yennefer has done. Like it's okay and everything should be forgiven because she's a sort of mother character to Ciri. (Because I have a whole list of things I can't forgive Yennefer for, but that's beside the point as most Yen fans also have a list of things they can't forgive Triss for while I see most of those things as speculation or non-issues. So... yeah, I know I have a huge bias towards Triss)
Then again, I also don't understand why some people like and want to date characters of my own games that I wrote as hateful girls that should not be liked by the reader either. (such as Elain from Rosie's Innocence. She's a bully and yet so many people wanted her to have more content/wanted to be able to ditch Rosie for her. Same goes for Emily in this game. Can't image why anyone would want to date her, but some people have requested it) Everyone has their own taste I guess...
And I did promised I'd get back to why I respect the games more because I read the books fore it, didn't I? Well... for me the games fixed almost every issue I had with the books. I openly admit that I was not a fan of the books. I have read tons and tons of fantasy novels I liked more. The character and world just didn't do it for me. But the games fixed that. The issues I had with the characters and world for the most part weren't there in games. For me it looked like they tweaked a few things about the world that the book was trying to go for. The books were going for a very gray mortality to everything, but I don't think they succeed in that. In my opinion the games just do it better, maybe because you have control over the actions of Geralt. I don't know. Take Nilfgaard and the Scoia'tael for example. Sorry, but they aren't 'gray' in the books. They are evil with no redeeming qualities for the most part. The games changed that for me. I related to the Scoia'tael much mroe in games than in the books where they were just about 100% evil. I feel the conflict more because I'm a part of it in the games. I actually got to talk to the elves, hear their story, instead of them just killing every human they came across like in the books. Same with Nilfgaard. Now that we can talk to some Nilfgaardians in Wild Hunt, I feel much more for them. In both cases, they are invaders and people don't like them. But I still like them more in the games because there are actually very likable Nilfgaardians that make you feel for them as well. That show you they don't like the situation either and aren't all invaders who want to burn everything down. But I think I'm getting a bit too negative about the books here. I enjoyed certain parts of them, but the games are what makes the Witcher great for me. If the games did not exist, I would simply not like the books or the Withcer franchise. But if the books didn't exist, I would still love the games.
But damn... this post is getting way too long. I'll have to end it here I think.