So in the books, how are "high level" Sorcerers kept in check at all, if they're so powerful and invincible?
How do the Nilfgaardians do it? Or the Northern rulers?
Sorry I do not entirely understand your question, maybe because english is not my first language. As far as I understand, your question was about how authorities control mages? Easy and simple, in the North they work together. as I understood from the books, mages was a minority, people fears them and calls them witches. That's why they can not openly rule the world, it would be a massacre of revolutionizing people, who do not want a witch to be their queen/king/lord, whatever. So they are gray cardinals, rulling from behind the throne. Why they are amendable to the kings or other authorities? Because it is in their interest, to be friendly with "big people", to rule, to control, not to be a crazy dudes and chicks, who is uncontrollable freaks and kills everybody, because they have powers, ha-ha-ha.
In Nilfgaard, there was a culture thing, that sorcerers was treated like a shit, to prevent them from ruling the country. This attitude has it difficulties for the mages, they should be very careful of what they speak or do. I think that was not because they could not blow up Emhyr with his throne, but because they are adequate and smart people, who knew where to cast a spell, and where to bow.
Isn't that a consistency in itself?
Why not? Yes for me.
They as a group did some seriously messed up stuff, and it's only through exploiting that fear
I will not start about how I hate how RED's handled it. I will look into the lore. The Witch Hund did not start because of retarded Radovid and silly king assassinations, but because of Ithlinne prophecy - they killed a lot of women, because they wanted to kill the Destroyer ( I presume it is something to do with Ciri, it was not explained by Sapkowski). It is more acceptable reason to raise a crowd against sorceresses than in-games "look, a king-assassins, bad girls/boys, hate them"! How many people would think - "one less, one more, I do not care". Or "Yay, I hated that fat shit and his stupid wars for a piece of land/royal whore, where my dad, uncle and two brothers died"? There should be the reason, and there is a very weak one in games.
I don't know, may be, some sadistic psychopaths enjoy that scene where horribly beaten and tortured woman, who is a likable character too, dies in the most horrific way...
Oh, yes. As a fan of Sile, I was horrified what devs did with her. It's a sick way to treat her like that, because at first she was not a bad character in the books. And make her die in a three sickening ways - like torn her to pieces in the W2 or see her tortured and killed without a hope to heal and live? Well, that was awful.
Sila was a murderer among other things.
So was Geralt, Letho, Zoltan, Triss, Yen, Radovid, Henselt and so on. Let's torture them too, why not? Why Letho, who was not only murderer of a two kings, but also traitor is given a chance to live and Sile is not? Because he is all white and fluffy inside?