I wouldn't say that for simple reason. I have no proof of that
And this changes what? Sapkowski also said that "The Lady of the Lake" is the end and there will be no continuation, yet CDPR made some great games which we love and many people consider them as their headcanon continuation. I don't see why some things from "SE, SB" can't be adapted in a way that treat itself seriously. Like Eskel and Triss thing.
Yet highlights Eskel's nice gentleman feature he shows Triss. When we put together this with his attitude towards Triss in TW1 (he trusts her despite what he thinks about sorceresses), it's something to build on. I wrote "slightly built", not "they are meant to be together since BoE".
And this is another reason that Eskel isn't sure that Triss could be with him and he tells that to Geralt in our adventure. For the player to think through and choose. Can Triss be free of Geralt? What would has to happen to make it so? Is Eskel enough? Is Triss a good choice for Eskel? Is it, as you said, a delusion, because Eskel just lost his mentor and seeks some relationship to fix a hole?
In the trilogy players got a choice to be with Triss, even if Geralt's only choice was always Yen. And players who think Geralt and Triss don't belong together can choose that. And if you think Eskel and Triss don't belong together, then choose this. It's not fixed ending, we made a choice there for purpose. Because we are aware of everything you states. And we mentioned all of it in our adventure. But we think that there is enough between those two to make their relationship possible and that there are people who thinks similarly (and from the comments we recieved there are at least some).