I get what Corky is saying. He's saying that it's easier to play a villain like the Joker because you really have no restraints on how to act the part, you can pretty much just create your own character and highlight the more vibrant aspects of the character, where as with a more normal role, you're forced to restrict your ability to act in the confines of a normal person, therefore it requires more effort to make it come off as believable.
But regardless, I don't agree with Corky at all. What makes Heath's Joker such an amazing performance is not the fact that he simply played an evil character well, it's because his performance was able to trigger such a strong, and powerful emotional response in the audience. Heath's performance could have gone very wrong, but the fact that he was able to do it in such a way that perfectly captured the essence of the character is what makes his performance so great. Every line, every way he pronounced the words, the way he elevated his voice, smallest details down to the very syllables of the words and the smallest mannerisms, they all worked together in such a perfect way that the audience was truly able to see a character unlike anything they've ever seen before.
It's easy to play a villain, but it's f*cking hard to make a villain iconic and memorable like Heath did. Which is why his performance is so great. With art, sometimes it's not about how you do it, it's about the way the audience perceives the way you do it, and in this case, the audience was blown away, thereby making Heath's performance incredible.
