Conjurer's Candle and Shady Vendor were very popular in almost every SY deck, so they were nerfed. Nerfed to the abyss, pulling the whole faction with it. But I understand – the devs do not like cards that are overused.
At some point, Simlas and the dwarf duo – Zoltan & Munro were obnoxiously popular in ST decks due to the lack of consistently performing high-end ST cards. They were nerfed, probably deservedly so. The nerf to dwarves made this archetype a subpar, but who cares – the devs do not like overused cards, so it is understandable.
Just after introduction Sove was shaking the meta. It was used in almost any SK deck, even if it wasn't Patricidal Fury (which it was at that time). So it was nerfed, as the devs do not like overused cards. Fully understandable.
Aerondight was immensely popular in its first seasons and it was deadly with Golden Nekker, so due to public unrest it was nerfed and is (probably) in a good spot right now. Ah, and the devs do not like overused cards, so yet another argument for the nerf.
So can anyone explain me how it is even possible that Vilgefortz, who is present in ~95% of NG decks hasn't been touched like forever? Imperial formation? Vilgefortz. Double Cross? Vilgefortz. Tactical Decision? Yes, Vilgefortz. Imprisonment? Of course – Vilgefortz. And for whatever reason this isn't considered as "overused". I am clueless.
Source: https://www.reddit.com/r/gwent/comments/125y8vs/a_bit_of_a_rant_but_a_deserved_one_i_think/