And what I wished here is some player input: ability to verify (through optional investigation - subquests - completed earlier) what Letho is saying and challenging his position. To be a really active member of this conversation. To do something. To have prepared for it and not take everything at face-value.
And how do you want Geralt to verify what Letho said, when it happened in Nilfgaard months prior?
And it would have taken from the mystery of it, if Geralt can find out. And it would have made everyone else who trusted Letho incompetent, if they could have figured out his intentions.
As it is Geralt just stands there while the lore-dispensers is talking.
No, he's the one who tells Letho of the Wild Hunt. It's not completely one-sided.
In other words, instead of pursuing his own goals, he aids everyone else, resulting in him not learning anything about the actual things that mattered to him personally most from the start.
He did pursue his own goals, but if you hadn't noticed, Letho was completely outside his grasp in Act 2 and Act 3. It was not possible for him. But he did pursue, or can pursue, his own goals in Act 2 by retrieving his memory (which does reveal his past with Letho), and Act 3 saving Triss. Heck, in Act 2, he discovers that Letho was working with Sile (and on Roche's path, sees him, Serrit and Auckes).
The game's story was much bigger than Letho. Letho was the catalyst that created the chaos Geralt has to deal with. To forget that, is to ignore Letho's entire involvement in the story, and to weaken the foreshadowing of the war.
So I completely disagree. Geralt discovers about Letho as much as he needed to prior the conversation. Letho was not the center of the plot, nor necessarily Geralt's main motivation even by the middle of the game. Heck, Geralt can even tell Triss that he's willing to drop the whole hunt.