I don't 'weak' is the right word,maybe not more fleshed out (but in the end,who really cares *do I need to know about Hitler;Stalin* to understand that they are evil?)?
Actually yes, Hitler and Stalin had historically-driven motivations. Just knowing that they're "evil" does not inform how they came to power, who supported them and why, why they had the success level they did in their plans, and why and where they ultimately failed and succeeded.
Here's two versions of history circa 1941:
1) Japan attacked Pearl Harbour because they are evil cowards.
2) Japan had no internal oil supplies, the US was refusing requests to negotiate, and they needed to acquire some pacific territories to acquire oil. So they bombed Pearl Harbour as an (ultimately failed) attempt to buy enough time to consolidate the pacific.
Let me know which version you find more interesting, the relatively trivialised description, or the motivation-driven explanation.
It's not. It worked for the Joker. He is just evil. Malekith wasn't just "evil", he wanted revenge as well, he was motivated by something. He's more than just evil, he could potentially be justified.
No, the Joker was not "just evil" in the Dark Knight. He had a point and he fit the themes of the movie.
He emerges in a coherent manner: Batman is winning the fight against the mob, and thus they are becoming more desperate and resorting to more extreme tactics, and thus they empower a maniac, that makes sense.
And as the mob had to respond to Batman, Batman has to respond to the joker. This is a villain that just won't stop. The entire movie he gets worse and worse. He goes from the trivial act of robbing a bank, to moving in on the mob meeting and showing up with an explosive vest, to crashing the Wayne fundraiser, to the scene in the prison. Batman goes nuts in the interrogation room, and the Joker just won't budge. He just keeps laughing. Because of that Batman ends up compromised and uses the cell phone trick, and ends up having to kill Harvey. The Joker has a real impact on the world and on the other characters (Batman, Rachel, Harvey, the mob, etc), whereas Malakeith had no impact on Thor, Jane, Loki, etc.
The Joker is also intelligent. He predicts that Batman goes to Hong Kong, and he does. He ends up taking over the mob. He figures out that Batman loves Rachel Dawes. He figures out that he would rather keep Batman alive and even help protect his hidden identity ("If this man is still alive in one hour, I'm blowing up a major Gotham hospital"), whereas in the early part of the movie he just said "give me half your money to kill Batman". Oh yeah, and by burning the money, he shows that he's evolved as a character.
Finally, he has great lines and an actual philosophical point:
“If, tomorrow, I tell the press that, like, a gang banger will get shot, or a truckload of soldiers will be blown up, nobody panics, because it’s all ‘part of the plan’. But when I say that one little old mayor will die, well then everyone loses their minds!”
That isn't "just evil", it's a relevant and cogent diatribe about the distribution of power in society, that speaks both to contemporary America and Gotham as constructed in the Nolanverse.