Acting versus directing

Intellectually I know that many movies feature a lot of improvisation, and actor input, so much that that's a major factor in deciding what goes on in the movie. Maybe most of them. But I know that other movies are largely determined by the writer, director, and producer, and I have a mental predisposition to emphasize those factors. I imagine that the actors tend to get too much credit for "creating" the character, and then wonder if I'm wrong about it.

It's an overly simplistic viewpoint to think of it this way, but it's a skeleton to build from:

• The writer decides who the characters are.
  
• The director interprets what the writer intended and figures out how to depict it.
  
• The actor uses various techniques to express the internal states, motivations, emotions, etc. of the character to fit the director's idea.
  

The way this is too simplistic is particularly in how the actors inevitably will bounce ideas back to the director, and the writer can get in the mix, and sometimes several of these are the same people, and there's other people mixed in. Some movies no doubt hew more closely to this and some barely touch it. But if a movie is like that, the audience tends to give almost all the credit to the actor for the character, whether that's fair or not. Let's consider Heath Ledger's much lauded portrayal of the Joker, which was quite rightly congratulated as a fantastic performance. I don't mean to take anything away from my respect for his acting when I say, isn't a lot of what we love about the character in that movie because of things the writer and director did? What made the Joker so great in that movie for me is partially how Ledger portrayed him, but it was just as much what he was portraying: the motivations he was given, the actions he chose, how it made his madness that much more compelling and eerie. Heath Ledger didn't, I assume, write the speech the Joker gave Harvey Dent about how he was like a dog chasing a truck but with no idea what he'd do with it if he ever caught it. Ledger didn't stage the scene where he burned a pile of money, or decide how the Joker's schemes would pit people against their own weaknesses, and why he'd do that. Ledger didn't decide that all his backstories would conflict, and what kind of little bit of twistedness each one would add to the mosaic. Ledger didn't decide why the Joker wasn't just a babbling fool whose sole source of menace was unpredictability, but was instead a truly disturbed and disturbing person, bent on making other people find the worst things inside them. What Heath Ledger did is take those creative decisions, and imbue them into a performance so we could see not just the words, but the mannerisms, expressions, inflections, etc. that made them seem real. That's an amazing gift, not least because no one has a clue how most of it works (though I wonder if Paul Ekman's work isn't starting to breach that barrier). But did he create the character, or just realize it? I would like to see Heath get all the (unfortunately posthumous) credit he deserves, but the other people involved deserve more credit than they get from most people, too. Of course, plenty of other movies aren't done the way I feel sure Christopher Nolan tends to do his. For instance, I was recently reading how almost none of Beverly Hills Cop has anything to do with the script: most of it was improvised, and some scenes in the movie were lifted straight out of auditions. Considering how, just two weeks before filming began, the movie was an action movie starring Sylvester Stallone, we can safely say Eddie Murphy truly did create Axel Foley and deserves almost all the credit for that. Probably most movies fall somewhere between these extremes, but most audience members give the actors credit as if every movie was made like Beverly Hills Cop (mostly because they see the actors, but not the rest of the people responsible).

What I wonder is, in real movies, how many tend more towards one end or the other, really? Are actors getting way too much credit, or only a little too much?