It pretty much comes down to this; power corrupts. Choosing your favourite king (because I'd agree with Foltest too) is really about picking the lesser evil when all are, in the grand scheme of things, cunts. And that extends to everyone in positions of power. Powerful sorceresses and sorcerers scheme, manipulate, and are cunts. Nilfgaard is a cunt empire. All the kings are cunts. Roche is a cunt. Iorveth is a cunt. Scoia'tael are terrorists. Order of the Flaming Rose are basically Reich SS. Saskia is the closest "good leader" you'll find. Even Roche, the bro that he is, isn't really a bro; his primary goal is not helping you but specifically helping Termeria, and he schemes/plots/acts on this through all three acts, and uses you where necessary to forward these advances. He knows Loredo is scheming with Henselt, and wants him dead and the Kaedwen spy captured so Flotsam can remain under Termerian control. He gets his way, and kills the spy while torturing him. He follows Henselt to pursue this lead and is a key part of the conspiracy against him, and given the opportunity (as well as vengeance) kills the king with his own hands. His primary goal in Loc Muinne is securing Anaïs and doing what he can to preserve Foltest's rule, even if it means allying with Radovid.
He's a bro, but he's still a ruthless, political lapdog through and through and his entire character arc is rooted in politics and Termeria. Which for a character like Geralt who's supposed to be somewhat politically distant is quite a rock and a hard place.
Really, Witchers are the only ones with 'power' who've avoided abusing it and as a result it's got them nowhere. They're poor outcasts in a world that's rejecting them. No empires, no authority. In many ways Geralt has nothing, and the cunts have everything.
Well, all witchers except Letho anyway. I also figure most people just don't want to admit Geralt's true bro is Dandelion.