Haha! I don't think there's much to worry about. Taking one's coffee "black" is an actual expression; I would assume the "blacker" part is a result of the language barrier, and Daniel simply means no "additives" like cream or milk.
Because ultimately, Daniel isn't coercing Lana. His drugging Alex is nothing new, as he notes himself when recalling the events of Chapter 6. Daniel's aggressive, but he loves Lana. Uncle Peter, on the other hand, is a consequence of poor writing. When first introduced, he's presented as a doting, flattering, yet slightly mischievous and manipulative uncle. However, since Daval proceeded with his inclusion despite the protests of his subscribers, he mutated Uncle Peter's personality to that which would assure the fan base that there'd be no possible extended relationship between Sarah and her uncle. In other words, Daval turned Uncle Peter from someone who was constantly complimenting Sarah (something Sarah even notes had been going on since she lived with him in her youth) to someone who berates her and coerces her into sex--although, whether Uncle Peter "coerces" Sarah is up for debate. And if I remember correctly, in Chapter 6 of MT, Uncle Peter tells Aaron something to the effect of "all women are bitches..." in the hopes of having Aaron not dwell on what he witnessed, but instead seize opportunities to have sex with them when they arise. (And thus imply that Uncle Peter thinks of his own niece as nothing more than a bitch.) And now, even in his own comic, Peter is still an A-hole, of the highest order, the reasons for which are entirely unnecessary.
Uncle Peter's unlikable because Daval made him that way, and it's easier to target him because his appearance suggests creepy, ugly, old pervert. Daniel on the other hand has a decent appearance for a young male his age, and comes off more as "brazen" than "A-hole."