Doom is not noble. Doom is the furthest thing from noble. Would a noble man send a child to Hell? Kill his true love and wear her skin as armor? Imprint his own personality over that of his adopted son so as to cheat death? Doom knows how to play to a crowd; he knows he's impressive and badass and cool, and he knows that those things are seductive and that people will want to believe he's a good guy, deep down inside. Doom is not good and Doom is not noble. He's facist, he's obsessive, and he's utterly without mercy. If Doom shows signs of nobility it's either part of a scheme or just because it amuses him. Even when he takes over the world and creates a utopia -- which he's done several times -- he always gives it up and lets the world descend back into a ****hole because he gets bored. Even the Latverians he only cares about insofar as their apparent well-being and health reflects well on him. Doom is all EGO, capitol letters, all the time.
Namor falls into the Well-Intentioned Extremist camp, alongside Magneto when he's well-written. Namor is a king, and has responsibilities, and puts his people first. He's also arrogant and violent and not above chasing Sue Storm's very-married tail.
Cackling, kitten-eating maniacs tend to be boring -- I mean, really, does anyone actually care about Carnage? Anyone? At least Venom has personality and a twisted sense of right and wrong. And giving a supervillain an interesting backstory can be far and away the best thing that ever happened to them. Kang was your standard world-conquering supervillain until the Iron Lad retcon, which established him as someone who's instincts led him towards heroism, but found himself doomed to play the role of villain.