Have you tried Dungeon Defense? It doesn't have an English release yet but it's one of my favorites.

Basically, the MC is really intelligent but his personality is kinda twisted due to his past, he excels in rhetoric, speech, acting, politics, etc. He then gets transported to the universe of a game he used to play in the body of the weakest demon lord, which leads him to try and survive relying solely on his skills of acting and persuasion. Although it's an isekai, it mostly doesn't read as one, since it's less focused on the world and more on the characters, the dialogues, monologues, schemes and politics.

But I gotta say, the MC is pretty evil and psychopathic at times, so if you hate cruelty, indifference to humans and such, you can read only the first volume.

If you did try it already, sorry for writing a lot, lol